
KSZ8081RNA/RND
10BASE-T/100BASE-TX PHY with RMII 

Support
Features
• Single-Chip 10BASE-T/100BASE-TX IEEE 802.3 

Compliant Ethernet Transceiver
• RMII v1.2 Interface Support with a 50 MHz Refer-

ence Clock Output to MAC, and an Option to 
Input a 50 MHz Reference Clock

• RMII Back-to-Back Mode Support for a 100 Mbps 
Copper Repeater

• MDC/MDIO Management Interface for PHY Reg-
ister Configuration

• Programmable Interrupt Output
• LED Outputs for Link and Activity Status Indica-

tion
• On-Chip Termination Resistors for the Differential 

Pairs
• Baseline Wander Correction
• HP Auto MDI/MDI-X to Reliably Detect and Cor-

rect Straight-Through and Crossover Cable Con-
nections with Disable and Enable Option

• Auto-Negotiation to Automatically Select the 
Highest Link-Up Speed (10/100 Mbps) and 
Duplex (Half/Full)

• Power-Down and Power-Saving Modes
• LinkMD® TDR-Based Cable Diagnostics to Iden-

tify Faulty Copper Cabling
• Parametric NAND Tree Support for Fault Detec-

tion Between Chip I/Os and the Board
• HBM ESD Rating (6 kV)
• Loopback Modes for Diagnostics
• Single 3.3V Power Supply with VDD I/O Options 

for 1.8V, 2.5V, or 3.3V
• Built-In 1.2V Regulator for Core
• Available in 24-pin 4 mm x 4 mm QFN Package

Target Applications
• Game Consoles
• IP Phones
• IP Set-Top Boxes
• IP TVs
• LOM
• Printers
 2016 Microchip Technology Inc.  DS00002199A-page 1

S

MICROCHIP
�

KSZ8081RNA/RND
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DS00002199A-page 2   2016 Microchip Technology Inc.

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 2016 Microchip Technology Inc.  DS00002199A-page 3

KSZ8081RNA/RND
Table of Contents
1.0 Introduction ..................................................................................................................................................................................... 4
2.0 Pin Description and Configuration .................................................................................................................................................. 5
3.0 Functional Description .................................................................................................................................................................. 10
4.0 Register Descriptions .................................................................................................................................................................... 26
5.0 Operational Characteristics ........................................................................................................................................................... 35
6.0 Electrical Characteristics ............................................................................................................................................................... 36
7.0 Timing Diagrams............................................................................................................................................................................ 38
8.0 Reset Circuit .................................................................................................................................................................................. 42
9.0 Reference Circuits - LED Strap-In Pins ......................................................................................................................................... 43
10.0 Reference Clock - Connection and Selection .............................................................................................................................. 44
11.0 Magnetic - Connection and Selection .......................................................................................................................................... 45
12.0 Package Outlines......................................................................................................................................................................... 47
Appendix A: Data Sheet Revision History ........................................................................................................................................... 48
The Microchip Web Site ...................................................................................................................................................................... 49
Customer Change Notification Service ............................................................................................................................................... 49
Customer Support ............................................................................................................................................................................... 49
Product Identification System ............................................................................................................................................................. 50



KSZ8081RNA/RND

DS00002199A-page 4   2016 Microchip Technology Inc.

1.0 INTRODUCTION

1.1 General Description
The KSZ8081RNA/RND is a single-supply 10BASE-T/100BASE-TX Ethernet physical-layer transceiver for transmis-
sion and reception of data over standard CAT-5 unshielded twisted pair (UTP) cable.

The KSZ8081RNA/RND is a highly-integrated PHY solution. It reduces board cost and simplifies board layout by using
on-chip termination resistors for the differential pairs and by integrating a low-noise regulator to supply the 1.2V core,
and by offering 1.8/2.5/3.3V digital I/O interface support.

The KSZ8081RNA/RND offers the Reduced Media Independent Interface (RMII) for direct connection to RMII-compliant
MACs in Ethernet processors and switches.

As the power-up default, the KSZ8081RNA/RND uses a 25 MHz crystal to generate all required clocks, including the
50 MHz RMII reference clock output for the MAC. The KSZ8081RND is the version that takes in the 50 MHz RMII ref-
erence clock as the power-up default. 

To facilitate system bring-up and debugging in production testing and in product deployment, parametric NAND tree sup-
port enables fault detection between KSZ8081RNA/RND I/Os and the board. LinkMD® TDR-based cable diagnostics
identify faulty copper cabling.

The KSZ8081RNA and KSZ8081RND are available in 24-pin, lead-free QFN packages.

FIGURE 1-1: SYSTEM BLOCK DIAGRAM

KSZ8081RNA

M
A

G
N

E
TI

C
S

RJ-45
CONNECTOR

MEDIA TYPES:
   10BASE-T
   100BASE-TX

O
N

-C
H

IP
 T

E
R

M
IN

A
TI

O
N

 
R

E
S

IS
TO

R
S

RMII

MDC/MDIO 
MANAGEMENT

XO XI

25MHz 
XTAL

22pF 22pF 

10/100Mbps
RMII MAC

50MHz
REF_CLK



KSZ8081RNA/RND
2.0 PIN DESCRIPTION AND CONFIGURATION

FIGURE 2-1: 24-QFN PIN ASSIGNMENT (TOP VIEW)

1

2

3

4

5

6

18

17

16

15

14

13

24 23 22 21 20 19

7 8 9 10 11 12

PADDLE GROUND
(ON BOTTOM OF CHIP)

VDD_1.2

VDDA_3.3

RXM

RXP

TXM

TXP

INTRP

RXER

REF_CLK

CRS_DV/
PHYAD[1:0]

VDDIO

RXD0

R
S

T#

LE
D

0 
/

A
N

E
N

_S
P

E
E

D

G
N

D

TX
D

1

TX
D

0

TX
E

N

X
O X
I

R
E

X
T

M
D

IO

M
D

C

R
X

D
1

 2016 Microchip Technology Inc.  DS00002199A-page 5



KSZ8081RNA/RND
TABLE 2-1: SIGNALS - KSZ8081RNA/RND

Pin 
Number

Pin
Name

Type
Note
2-1

Description

1 VDD_1.2 P 1.2V Core VDD (power supplied by KSZ8081RNA/KSZ8081RND). Decouple with 2.2 µF and 0.1 µF capacitors to ground.

2 VDDA_3.3 P 3.3V Analog VDD.

3 RXM I/O Physical Receive or Transmit Signal (– differential).

4 RXP I/O Physical Receive or Transmit Signal (+ differential).

5 TXM I/O Physical Transmit or Receive Signal (– differential).

6 TXP I/O Physical Transmit or Receive Signal (+ differential).

7 XO O Crystal Feedback for 25 MHz Crystal. This pin is a no connect if an oscillator or external clock source is used.

8 XI I

RMII – 25 MHz Mode: 25 MHz ±50 ppm Crystal/Oscillator/External Clock 
Input 
RMII – 50 MHz Mode: 50 MHz ±50 ppm Oscillator/External Clock Input
For unmanaged mode (power-up default setting):
– KSZ8081RNA takes in the 25 MHz crystal/clock on this pin.
– KSZ8081RND takes in the 50 MHz clock on this pin.

After power-up, both the KSZ8081RNA and KSZ8081RND can be pro-
grammed to either the 25 MHz mode or 50 MHz mode using PHY Register 
1Fh Bit [7].
See also REF_CLK (Pin 16).

9 REXT I Set PHY Transmit Output Current. Connect a 6.49 kΩ resistor to ground on this pin.

10 MDIO Ipu/Opu
Management Interface (MII) Data I/O. This pin has a weak pull-up, is open-
drain, and requires an external 1.0 kΩ pull-up resistor.

11 MDC Ipu Management Interface (MII) Clock Input. This clock pin is synchronous to the MDIO data pin.

12 RXD1 Ipd/O RMII Receive Data Output[1] (Note 2-2).

13 RXD0 Ipu/O RMII Receive Data Output[0] (Note 2-2).

14 VDDIO P 3.3V, 2.5V, or 1.8V Digital VDD.

15 CRS_DV/PHYAD[1:0] Ipd/O

RMII Mode: Carrier Sense/Receive Data Valid Output.
Config. Mode: The pull-up/pull-down value is latched as PHYAD[1:0] at the 
de-assertion of reset. 
See the Strapping Options section for details.
DS00002199A-page 6   2016 Microchip Technology Inc.



KSZ8081RNA/RND
16 REF_CLK Ipd/O

RMII – 25 MHz Mode: This pin provides the 50 MHz RMII reference clock out-
put to the MAC.
RMII – 50 MHz Mode: This pin is a no connect.
For unmanaged mode (power-up default setting), 
– KSZ8081RNA is in RMII – 25 MHz mode and outputs the 50 MHz RMII ref-
erence clock on this pin.
– KSZ8081RND is in RMII – 50 MHz mode and does not use this pin.

After power-up, both KSZ8081RNA and KSZ8081RND can be programmed 
to either 25 MHz mode or 50 MHz mode using PHY Register 1Fh Bit [7].
See also XI (Pin 8).

17 RXER Ipd/O

RMII Receive Error Output. 
At the de-assertion of reset, this pin needs to latch in a pull-down value for 
normal operation. If MAC side pulls this pin high, see Register 16h, Bit [15] for 
solution. It is better having an external pull-down resistor to avoid MAC side 
pulls this pin high.

18 INTRP Ipu/Opu
Interrupt Output: Programmable interrupt output. This pin has a weak pull-up, 
is open drain, and requires an external 1.0 kΩ pull-up resistor.

19 TXEN I RMII Transmit Enable Input.

20 TXD0 I RMII Transmit Data Input [0] (Note 2-3).

21 TXD1 I/O RMII Transmit Data Input [1] (Note 2-3). NAND Tree Mode: NAND Tree output pin.

22 GND GND Ground.

23 LED0/ANEN_SPEED Ipu/O

LED Output: Programmable LED0 Output.
Config. Mode: Latched as auto-negotiation enable (Register 0h, Bit [12]) and 
Speed (Register 0h, Bit [13]) at the de-assertion of reset. See the Strapping 
Options section for details. 
The LED0 pin is programmable using Register 1Fh bits [5:4], and is defined 
as follows:

LED Mode = [00]

Link/Activity Pin State LED Definition

No Link High OFF

Link Low ON

Activity Toggle Blinking

LED Mode = [01]

Link Pin State LED Definition

No Link High OFF

Link Low ON

LED Mode = [10], [11]: Reserved

24 RST# Ipu Chip Reset (active-low).

TABLE 2-1: SIGNALS - KSZ8081RNA/RND (CONTINUED)

Pin 
Number

Pin
Name

Type
Note
2-1

Description
 2016 Microchip Technology Inc.  DS00002199A-page 7



KSZ8081RNA/RND
Note 2-1 P = power supply
GND = ground
I = input
O = output
I/O = bi-directional
Ipu = Input with internal pull-up (see Section 6.0, "Electrical Characteristics" for value).
Ipu/O = Input with internal pull-up (see Section 6.0, "Electrical Characteristics" for value) during
power-up/reset; output pin otherwise.
Ipd/O = Input with internal pull-down (see Electrical Characteristics for value) during power-up/reset;
output pin otherwise.
Ipu/Opu = Input with internal pull-up (see Electrical Characteristics for value) and output with internal
pull-up (see Electrical Characteristics for value).

Note 2-2 RMII RX Mode: The RXD[1:0] bits are synchronous with the 50 MHz RMII Reference Clock. For each
clock period in which CRS_DV is asserted, two bits of recovered data are sent by the PHY to the
MAC.

Note 2-3 RMII TX Mode: The TXD[1:0] bits are synchronous with the 50 MHz RMII Reference Clock. For each
clock period in which TXEN is asserted, two bits of data are received by the PHY from the MAC.

Paddle GND GND Ground.

TABLE 2-1: SIGNALS - KSZ8081RNA/RND (CONTINUED)

Pin 
Number

Pin
Name

Type
Note
2-1

Description
DS00002199A-page 8   2016 Microchip Technology Inc.



KSZ8081RNA/RND

The PHYAD[1:0] strap-in pin is latched at the de-assertion of reset. In some systems, the RMII MAC receive input pins
may drive high/low during power-up or reset, and consequently cause the PHYAD[1:0] strap-in pin, a shared pin with
the RMII CRS_DV signal, to be latched to the unintended high/low state. In this case an external pull-up (4.7 kΩ) or pull-
down (1.0 kΩ) should be added on the PHYAD[1:0] strap-in pin to ensure that the intended value is strapped-in correctly.

Note 2-4 Ipu/O = Input with internal pull-up (see Electrical Characteristics for value) during power-up/reset;
output pin otherwise.
Ipd/O = Input with internal pull-down (see Electrical Characteristics for value) during power-up/reset;
output pin otherwise.

TABLE 2-2: STRAP-IN OPTIONS - KSZ8081RNA/RND

Pin Number Pin Name TypeNote 2-4 Description

15 PHYAD[1:0] Ipd/O

The PHY Address is latched at the de-assertion of reset and is con-
figurable to either one of the following two values:
Pull-up = PHY Address is set to 00011b (0x3h)
Pull-down (default) = PHY Address is set to 00000b (0x0h)

PHY Address Bits [4:2] are set to 000 by default.

23 ANEN_SPEED Ipu/O

Auto-Negotiation Enable and SPEED Mode
Pull-up (default) = Enable Auto-Negotiation and set 100 Mbps Speed
Pull-down = Disable Auto-Negotiation and set 10 Mbps Speed

At the de-assertion of reset, this pin value is latched into Register 0h 
Bit [12] for Auto-negotiation enable/disable, Register 0h Bit [13] for 
the speed select, and Register 4h (Auto-Negotiation Advertisement) 
for the speed capability support.
 2016 Microchip Technology Inc.  DS00002199A-page 9



KSZ8081RNA/RND
3.0 FUNCTIONAL DESCRIPTION
The KSZ8081RNA is an integrated, single 3.3V supply, fast Ethernet transceiver. It is fully compliant with the IEEE 802.3
Specification, and reduces board cost and simplifies board layout by using on-chip termination resistors for the two dif-
ferential pairs and by integrating the regulator to supply the 1.2V core.

On the copper media side, the KSZ8081RNA supports 10BASE-T and 100BASE-TX for transmission and reception of
data over a standard CAT-5 unshielded twisted pair (UTP) cable, and HP Auto MDI/MDI-X for reliable detection of and
correction for straight-through and crossover cables.

On the MAC processor side, the KSZ8081RNA offers the Reduced Media Independent Interface (RMII) for direct con-
nection with RMII-compliant Ethernet MAC processors and switches

The MII management bus option gives the MAC processor complete access to the KSZ8081RNA control and status
registers. Additionally, an interrupt pin eliminates the need for the processor to poll for PHY status change.

As the power-up default, the KSZ8081RNA uses a 25 MHz crystal to generate all required clocks, including the 50 MHz
RMII reference clock output for the MAC. The KSZ8081RND version uses the 50 MHz RMII reference clock as the
power-up default. 

The KSZ8081RNA/RND is used to refer to both KSZ8081RNA and KSZ8081RND versions in this data sheet.

3.1 10BASE-T/100BASE-TX Transceiver

3.1.1 100BASE-TX TRANSMIT
The 100BASE-TX transmit function performs parallel-to-serial conversion, 4B/5B encoding, scrambling, NRZ-to-NRZI
conversion, and MLT3 encoding and transmission. 

The circuitry starts with a parallel-to-serial conversion, which converts the MII data from the MAC into a 125 MHz serial
bit stream. The data and control stream is then converted into 4B/5B coding and followed by a scrambler. The serialized
data is further converted from NRZ-to-NRZI format, and then transmitted in MLT3 current output. The output current is
set by an external 6.49 kΩ 1% resistor for the 1:1 transformer ratio. 

The output signal has a typical rise/fall time of 4 ns and complies with the ANSI TP-PMD standard regarding amplitude
balance, overshoot, and timing jitter. The wave-shaped 10BASE-T output is also incorporated into the 100BASE-TX
transmitter.

3.1.2 100BASE-TX RECEIVE
The 100BASE-TX receiver function performs adaptive equalization, DC restoration, MLT3-to-NRZI conversion, data and
clock recovery, NRZI-to-NRZ conversion, de-scrambling, 4B/5B decoding, and serial-to-parallel conversion. 

The receiving side starts with the equalization filter to compensate for inter-symbol interference (ISI) over the twisted
pair cable. Because the amplitude loss and phase distortion is a function of the cable length, the equalizer must adjust
its characteristics to optimize performance. In this design, the variable equalizer makes an initial estimation based on
comparisons of incoming signal strength against some known cable characteristics, then tunes itself for optimization.
This is an ongoing process and self-adjusts against environmental changes such as temperature variations.

Next, the equalized signal goes through a DC-restoration and data-conversion block. The DC-restoration circuit com-
pensates for the effect of baseline wander and improves the dynamic range. The differential data-conversion circuit con-
verts MLT3 format back to NRZI. The slicing threshold is also adaptive.

The clock-recovery circuit extracts the 125 MHz clock from the edges of the NRZI signal. This recovered clock is then
used to convert the NRZI signal to NRZ format. This signal is sent through the de-scrambler, then the 4B/5B decoder.
Finally, the NRZ serial data is converted to MII format and provided as the input data to the MAC.

3.1.3 SCRAMBLER/DE-SCRAMBLER (100BASE-TX ONLY)
The scrambler spreads the power spectrum of the transmitted signal to reduce electromagnetic interference (EMI) and
baseline wander. The de-scrambler recovers the scrambled signal.

3.1.4 10BASE-T TRANSMIT
The 10BASE-T drivers are incorporated with the 100BASE-TX drivers to allow for transmission using the same mag-
netic. The drivers perform internal wave-shaping and pre-emphasis, and output 10BASE-T signals with typical ampli-
tude of 2.5V peak. The 10BASE-T signals have harmonic contents that are at least 27 dB below the fundamental
frequency when driven by an all-ones Manchester-encoded signal.
DS00002199A-page 10   2016 Microchip Technology Inc.



KSZ8081RNA/RND

3.1.5 10BASE-T RECEIVE
On the receive side, input buffer and level detecting squelch circuits are used. A differential input receiver circuit and a
phase-locked loop (PLL) performs the decoding function. The Manchester-encoded data stream is separated into clock
signal and NRZ data. A squelch circuit rejects signals with levels less than 400 mV, or with short pulse widths, to prevent
noise at the RXP and RXM inputs from falsely triggering the decoder. When the input exceeds the squelch limit, the PLL
locks onto the incoming signal and the KSZ8081RNA/RND decodes a data frame. The receive clock is kept active
during idle periods between data receptions.

3.1.6 PLL CLOCK SYNTHESIZER
The KSZ8081RNA/RND in RMII – 25 MHz Clock mode generates all internal clocks and all external clocks for system
timing from an external 25 MHz crystal, oscillator, or reference clock. For the KSZ8081RNA/RND in RMII – 50 MHz
clock mode, these clocks are generated from an external 50 MHz oscillator or system clock.

3.1.7 AUTO-NEGOTIATION
The KSZ8081RNA/RND conforms to the auto-negotiation protocol, defined in Clause 28 of the IEEE 802.3 Specifica-
tion. 

Auto-negotiation allows unshielded twisted pair (UTP) link partners to select the highest common mode of operation. 

During auto-negotiation, link partners advertise capabilities across the UTP link to each other and then compare their
own capabilities with those they received from their link partners. The highest speed and duplex setting that is common
to the two link partners is selected as the mode of operation. 

The following list shows the speed and duplex operation mode from highest to lowest priority.

• Priority 1: 100BASE-TX, full-duplex
• Priority 2: 100BASE-TX, half-duplex
• Priority 3: 10BASE-T, full-duplex
• Priority 4: 10BASE-T, half-duplex

If auto-negotiation is not supported or the KSZ8081RNA/RND link partner is forced to bypass auto-negotiation, then the
KSZ8081RNA/RND sets its operating mode by observing the signal at its receiver. This is known as parallel detection,
which allows the KSZ8081RNA/RND to establish a link by listening for a fixed signal protocol in the absence of the auto-
negotiation advertisement protocol.

Auto-negotiation is enabled by either hardware pin strapping (ANEN_SPEED, Pin 23) or software (Register 0h, Bit [12]). 

By default, auto-negotiation is enabled after power-up or hardware reset. After that, auto-negotiation can be enabled or
disabled by Register 0h, Bit [12]. If auto-negotiation is disabled, the speed is set by Register 0h, Bit [13], and the duplex
is set by Register 0h, Bit [8].

The auto-negotiation link-up process is shown in Figure 3-1.
 2016 Microchip Technology Inc.  DS00002199A-page 11



KSZ8081RNA/RND

FIGURE 3-1: AUTO-NEGOTIATION FLOW CHART

3.2 RMII Interface
The Reduced Media Independent Interface (RMII) specifies a low pin count Media Independent Interface (MII). It pro-
vides a common interface between physical layer and MAC layer devices, and has the following key characteristics:

• Pin count is 8 pins (3 pins for data transmission, 4 pins for data reception, and 1 pin for the 50 MHz reference 
clock).

• 10 Mbps and 100 Mbps data rates are supported at both half- and full-duplex.
• Data transmission and reception are independent and belong to separate signal groups.
• Transmit data and receive data are each 2 bits wide, a dibit.

3.2.1 RMII SIGNAL DEFINITION
Table 3-1 describes the RMII signals. Refer to RMII Specification v1.2 for detailed information.

START AUTO-NEGOTIATION

FORCE LINK SETTING

LISTEN FOR 10BASE-T 
LINK PULSES

LISTEN FOR 100BASE-TX
IDLES

ATTEMPT AUTO-
NEGOTIATION

LINK MODE SET

BYPASS AUTO-NEGOTIATION
AND SET LINK MODE

LINK MODE SET?

PARALLEL
OPERATIONNO

YES

YES

NO

JOIN FLOW
DS00002199A-page 12   2016 Microchip Technology Inc.



KSZ8081RNA/RND
3.2.1.1 Reference Clock (REF_CLK)
REF_CLK is a continuous 50 MHz clock that provides the timing reference for TXEN, TXD[1:0], CRS_DV, RXD[1:0],
and RX_ER.

For RMII – 25 MHz Clock Mode, the KSZ8081RNA/RND generates and outputs the 50 MHz RMII REF_CLK to the MAC
at REF_CLK (Pin 16).

For RMII – 50 MHz Clock Mode, the KSZ8081RNA/RND takes in the 50 MHz RMII REF_CLK from the MAC or system
board at XI (Pin 8) and leaves the REF_CLK (Pin 16) as no connect.

3.2.1.2 Transmit Enable (TXEN)
TXEN indicates that the MAC is presenting dibits on TXD[1:0] for transmission. It is asserted synchronously with the first
dibit of the preamble and remains asserted while all dibits to be transmitted are presented on the RMII. It is negated
before the first REF_CLK following the final dibit of a frame.

TXEN transitions synchronously with respect to REF_CLK.

3.2.1.3 Transmit Data[1:0] (TXD[1:0])
TXD[1:0] transitions synchronously with respect to REF_CLK. When TXEN is asserted, the PHY accepts TXD[1:0] for
transmission.

TXD[1:0] is 00 to indicate idle when TXEN is de-asserted. The PHY ignores values other than 00 on TXD[1:0] while
TXEN is de-asserted.

3.2.1.4 Carrier Sense/Receive Data Valid (CRS_DV)
The PHY asserts CRS_DV when the receive medium is non-idle. It is asserted asynchronously when a carrier is
detected. This happens when squelch is passed in 10 Mbps mode, and when two non-contiguous 0s in 10 bits are
detected in 100 Mbps mode. Loss of carrier results in the de-assertion of CRS_DV.

While carrier detection criteria are met, CRS_DV remains asserted continuously from the first recovered dibit of the
frame through the final recovered dibit. It is negated before the first REF_CLK that follows the final dibit. The data on
RXD[1:0] is considered valid after CRS_DV is asserted. However, because the assertion of CRS_DV is asynchronous
relative to REF_CLK, the data on RXD[1:0] is 00 until receive signals are properly decoded.

3.2.1.5 Receive Data[1:0] (RXD[1:0])
RXD[1:0] transitions synchronously with respect to REF_CLK. For each clock period in which CRS_DV is asserted,
RXD[1:0] transfers two bits of recovered data from the PHY.

RXD[1:0] is 00 to indicate idle when CRS_DV is de-asserted. The MAC ignores values other than 00 on RXD[1:0] while
CRS_DV is de-asserted.

TABLE 3-1: RMII SIGNAL DEFINITION

RMII Signal 
Name

Direction with 
Respect to PHY, 
KSZ8081 Signal

Direction with 
Respect to MAC Description

REF_CLK

Output (25 MHz 
Clock Mode)/

No Connect (50 MHz 
Clock Mode)

Input/
Input or No Connect

Synchronous 50 MHz reference clock for receive, trans-
mit, and control interface

TXEN Input Output Transmit Enable
TXD[1:0] Input Output Transmit Data[1:0]
CRS_DV Output Input Carrier Sense/Receive Data Valid
RXD[1:0] Output Input Receive Data[1:0]

RXER Output Input or Not Required Receive Error
 2016 Microchip Technology Inc.  DS00002199A-page 13



KSZ8081RNA/RND

3.2.1.6 Receive Error (RXER)
RXER is asserted for one or more REF_CLK periods to indicate that a symbol error (for example, a coding error that a
PHY can detect that may otherwise be undetectable by the MAC sub-layer) was detected somewhere in the frame being
transferred from the PHY.

RXER transitions synchronously with respect to REF_CLK. While CRS_DV is de-asserted, RXER has no effect on the
MAC.

3.2.1.7 Collision Detection (COL)
The MAC regenerates the COL signal of the MII from TXEN and CRS_DV.

3.2.2 RMII SIGNAL DIAGRAM – 25/50 MHZ CLOCK MODE
The KSZ8081RNA/RND RMII pin connections to the MAC for 25 MHz clock mode are shown in Figure 3-2. The con-
nections for 50 MHz clock mode are shown in Figure 3-3.

3.2.2.1 RMII – 25 MHz Clock Mode
The KSZ8081RNA is configured to RMII – 25 MHz clock mode after it is powered up or hardware reset with the following:

• A 25 MHz crystal connected to XI, XO (Pins 8, 7), or an external 25 MHz clock source (oscillator) connected to XI

The KSZ8081RND can optionally be configured to RMII – 25 MHz clock mode after it is powered up or hardware reset
and software programmed with the following:

• A 25 MHz crystal connected to XI, XO (Pins 8, 7), or an external 25 MHz clock source (oscillator) connected to XI
• Register 1Fh, Bit [7] programmed to ‘1’ to select RMII – 25 MHz clock mode

FIGURE 3-2: KSZ8081RNA/RND RMII INTERFACE (RMII - 25 MHZ CLOCK MODE)

'

KSZ8081RNA/RND

CRS_DV

RXD[1:0]

RXER

TXD[1:0]

RMII MAC

CRS_DV

RXD[1:0]

TXD[1:0]

RX_ER

REF_CLK

TXEN TX_EN

XI

REF_CLK

XO

25MHz
XTAL

22pF 22pF
DS00002199A-page 14   2016 Microchip Technology Inc.



KSZ8081RNA/RND

3.2.2.2 RMII – 50 MHz Clock Mode
The KSZ8081RND is configured to RMII – 50 MHz clock mode after it is powered up or hardware reset with the follow-
ing:

• An external 50 MHz clock source (oscillator) connected to XI (Pin 8)

The KSZ8081RNA can optionally be configured to RMII – 50 MHz clock mode after it is powered up or hardware reset
and software programmed with the following:

• An external 50 MHz clock source (oscillator) connected to XI (Pin 8)
• Register 1Fh, Bit [7] programmed to ‘1’ to select RMII – 50 MHz clock mode

FIGURE 3-3: KSZ8081RNA/RND RMII INTERFACE (RMII - 50 MHZ CLOCK MODE)

KSZ8081RNA/RND

CRS_DV

RXD[1:0]

RXER

TXD[1:0]

RMII MAC

CRS_DV

RXD[1:0]

TXD[1:0]

RX_ER

REF_CLK

TXEN TX_EN

XI

50MHz
OSC
 2016 Microchip Technology Inc.  DS00002199A-page 15



KSZ8081RNA/RND

3.3 Back-to-Back Mode – 100 Mbps Copper Repeater
Two KSZ8081RNA/RND devices can be connected back-to-back to form a managed 100BASE-TX copper repeater.

3.3.1 RMII BACK-TO-BACK MODE
In RMII back-to-back mode, a KSZ8081RNA/RND interfaces with another KSZ8081RNA/RND to provide a 100 Mbps
copper repeater solution.

The KSZ8081RNA/RND devices are configured to RMII back-to-back mode after power-up or reset, and software pro-
gramming, with the following:

• A common 50 MHz reference clock connected to XI (Pin 8)
• Register 1Fh, Bit [7] programmed to ‘1’ to select RMII – 50 MHz clock mode for KSZ8081RNA

KSZ8081RND is set to RMII – 50 MHz clock mode as the default after power up or hardware reset.

• Register 16h, Bits [6] and [1] programmed to ‘1’ and ‘1’, respectively, to enable RMII back-to-back mode.
• RMII signals connected as shown in Table 3-2.

FIGURE 3-4: KSZ8081RNA/RND AND KSZ8081RNA/RND RMII BACK-TO-BACK COPPER 
REPEATER

TABLE 3-2: RMII SIGNAL CONNECTION FOR RMII BACK-TO-BACK MODE (100BASE-TX 
COPPER REPEATER)

KSZ8081RNA/RND (100BASE-TX Copper)
[Device 1]

KSZ8081RNA/RND (100BASE-TX Copper)
[Device 2]

Pin Name Pin Number Pin Type Pin Name Pin Number Pin Type

CRS_DV 15 Output TXEN 19 Input
RXD1 12 Output TXD1 21 Input
RXD0 13 Output TXD0 20 Input
TXEN 19 Input CRS_DV 15 Output
TXD1 21 Input RXD1 12 Output
TXD0 20 Input RXD0 13 Output

KSZ8081RNA/RND
(COPPER MODE)

RXP/RXM

TXP/TXM

RxD

TxD

RxD

TxD

OSC

XI 

XI 

50MHz

TXP/TXM

RXP/RXM

(COPPER MODE)
KSZ8081RNA/RND
DS00002199A-page 16   2016 Microchip Technology Inc.



KSZ8081RNA/RND

3.4 MII Management (MIIM) Interface
The KSZ8081RNA/RND supports the IEEE 802.3 MII management interface, also known as the Management Data
Input/Output (MDIO) interface. This interface allows an upper-layer device, such as a MAC processor, to monitor and
control the state of the KSZ8081RNA/RND. An external device with MIIM capability is used to read the PHY status and/
or configure the PHY settings. More details about the MIIM interface can be found in Clause 22.2.4 of the IEEE 802.3
Specification.

The MIIM interface consists of the following:

• A physical connection that incorporates the clock line (MDC) and the data line (MDIO).
• A specific protocol that operates across the physical connection mentioned earlier, which allows the external con-

troller to communicate with one or more PHY devices.
• A set of 16-bit MDIO registers. Registers [0:8] are standard registers, and their functions are defined in the IEEE 

802.3 Specification. The additional registers are provided for expanded functionality. See the Register Map section 
for details.

The KSZ8081RNA/RND supports only two unique PHY addresses. The PHYAD[1:0] strapping pin is used to select
either 0h or 3h as the unique PHY address for the KSZ8081RNA/RND device.

PHY address 0h is defined as the broadcast PHY address according to the IEEE 802.3 Specification, and can be used
to read/write to a single PHY device, or write to multiple PHY devices simultaneously. For the KSZ8081RNA/RND, PHY
address 0h defaults to the broadcast PHY address after power-up, but PHY address 0h can be disabled as the broad-
cast PHY address using software to assign it as a unique PHY address.

For applications that require two KSZ8081RNA/RND PHYs to share the same MDIO interface with one PHY set to
address 0h and the other PHY set to address 3h, use PHY address 0h (defaults to broadcast after power-up) to set both
PHYs’ Register 16h, Bit [9] to ‘1’ to assign PHY address 0h as a unique (non-broadcast) PHY address.

Table 3-3 shows the MII management frame format for the KSZ8081RNA/RND.

3.5 Interrupt (INTRP)
INTRP (Pin 18) is an optional interrupt signal that is used to inform the external controller that there has been a status
update to the KSZ8081RNA/RND PHY register. Bits [15:8] of Register 1Bh are the interrupt control bits to enable and
disable the conditions for asserting the INTRP signal. Bits [7:0] of Register 1Bh are the interrupt status bits to indicate
which interrupt conditions have occurred. The interrupt status bits are cleared after reading Register 1Bh.

Bit [9] of Register 1Fh sets the interrupt level to active high or active low. The default is active low.

The MII management bus option gives the MAC processor complete access to the KSZ8081RNA/RND control and sta-
tus registers. Additionally, an interrupt pin eliminates the need for the processor to poll the PHY for status change.

3.6 HP Auto MDI/MDI-X
HP Auto MDI/MDI-X configuration eliminates the need to decide whether to use a straight cable or a crossover cable
between the KSZ8081RNA/RND and its link partner. This feature allows the KSZ8081RNA/RND to use either type of
cable to connect with a link partner that is in either MDI or MDI-X mode. The auto-sense function detects transmit and
receive pairs from the link partner and assigns transmit and receive pairs to the KSZ8081RNA/RND accordingly.

HP Auto MDI/MDI-X is enabled by default. It is disabled by writing a ‘1’ to Register 1Fh, Bit [13]. MDI and MDI-X mode
is selected by Register 1Fh, Bit [14] if HP Auto MDI/MDI-X is disabled.

An isolation transformer with symmetrical transmit and receive data paths is recommended to support Auto MDI/MDI-X.

Table 3-4 shows how the IEEE 802.3 Standard defines MDI and MDI-X.

TABLE 3-3: MII MANAGEMENT FRAME FORMAT FOR THE KSZ8081RNA/RND

Preamble Start of Frame

Read/
Write OP 

Code

PHY 
Address 
Bits[4:0]

REG 
Address 
Bits[4:0]

TA Data Bits[15:0] Idle

Read 32 1’s 01 10 000AA RRRRR Z0 DDDDDDDD_DDDDDDDD Z
Write 32 1’s 01 01 000AA RRRRR 10 DDDDDDDD_DDDDDDDD Z
 2016 Microchip Technology Inc.  DS00002199A-page 17



KSZ8081RNA/RND
3.6.1 STRAIGHT CABLE
A straight cable connects an MDI device to an MDI-X device, or an MDI-X device to an MDI device. Figure 3-5 shows
a typical straight cable connection between a NIC card (MDI device) and a switch or hub (MDI-X device).

3.6.2 CROSSOVER CABLE
A crossover cable connects an MDI device to another MDI device, or an MDI-X device to another MDI-X device.
Figure 3-6 shows a typical crossover cable connection between two switches or hubs (two MDI-X devices).

TABLE 3-4: MDI/MDI-X PIN DESCRIPTION
MDI MDI-X

RJ-45 Pin Signal RJ-45 Pin Signal

1 TX+ 1 RX+
2 TX– 2 RX–
3 RX+ 3 TX+
6 RX– 6 TX–

FIGURE 3-5: TYPICAL STRAIGHT CABLE CONNECTION

RECEIVE PAIR TRANSMIT PAIR

RECEIVE PAIR 

1

2

3

4

5

6

7

8

1 
2 
3 
4 
5 
6 
7 
8 

TRANSMIT PAIR

MODULAR CONNECTOR 
(RJ-45) 

NIC 

STRAIGHT 
CABLE

10/100 ETHERNET 
MEDIA DEPENDENT INTERFACE 

10/100 ETHERNET 
MEDIA DEPENDENT INTERFACE 

MODULAR CONNECTOR 
(RJ-45) 

HUB
(REPEATER OR SWITCH) 
DS00002199A-page 18   2016 Microchip Technology Inc.



KSZ8081RNA/RND
3.7 Loopback Mode
The KSZ8081RNA/RND supports the following loopback operations to verify analog and/or digital data paths.

• Local (digital) loopback
• Remote (analog) loopback

3.7.1 LOCAL (DIGITAL) LOOPBACK
This loopback mode checks the RMII transmit and receive data paths between the KSZ8081RNA/RND and the external
MAC, and is supported for both speeds (10/100 Mbps) at full-duplex.

The loopback data path is shown in Figure 3-7.

1. The RMII MAC transmits frames to the KSZ8081RNA/RND.
2. Frames are wrapped around inside the KSZ8081RNA/RND.
3. The KSZ8081RNA/RND transmits frames back to the RMII MAC.
4. Except the frames back to the RMII MAC, the transmit frames also go out from the copper port.

FIGURE 3-6: TYPICAL CROSSOVER CABLE CONNECTION

FIGURE 3-7: LOCAL (DIGITAL) LOOPBACK

RECEIVE PAIR RECEIVE PAIR

TRANSMIT PAIR

1

2

3

4

5

6

7

8

1

2

3

4

5

6

7

8

TRANSMIT PAIR

10/100 ETHERNET
MEDIA DEPENDENT INTERFACE

10/100 ETHERNET
MEDIA DEPENDENT INTERFACE

MODULAR CONNECTOR 
(RJ-45)

HUB
(REPEATER OR SWITCH)

CROSSOVER
CABLE

MODULAR CONNECTOR 
(RJ-45)

HUB
(REPEATER OR SWITCH)

RMII
MAC

RMII
PCS

(DIGITAL)

AFE

(ANALOG)

KSZ8081RNA/RND
 2016 Microchip Technology Inc.  DS00002199A-page 19



KSZ8081RNA/RND

The following programming action and register settings are used for local loopback mode:

For 10/100 Mbps loopback:

Set Register 0h,

Bit [14] = 1        // Enable local loopback mode

Bit [13] = 0/1     // Select 10 Mbps/100 Mbps speed

Bit [12] = 0        // Disable auto-negotiation 

Bit [8] = 1          // Select full-duplex mode

Follow the steps below if you don’t want the frames go out from the copper port in the local loopback.

1. Set register 1Fh bit [3] to ‘1’ to disable the transmitter.
2. Run local loopback test as above.
3. Set register 1Fh bit [3] to ‘0’ to enable the transmitter.

3.7.2 REMOTE (ANALOG) LOOPBACK
This loopback mode checks the line (differential pairs, transformer, RJ-45 connector, Ethernet cable) transmit and
receive data paths between the KSZ8081RNA/RND and its link partner, and is supported for 100BASE-TX full-duplex
mode only.

The loopback data path is shown in Figure 3-8.

1. The Fast Ethernet (100BASE-TX) PHY link partner transmits frames to the KSZ8081RNA/RND.
2. Frames are wrapped around inside the KSZ8081RNA/RND.
3. The KSZ8081RNA/RND transmits frames back to the Fast Ethernet (100BASE-TX) PHY link partner.

The following programming steps and register settings are used for remote loopback mode:

1. Set Register 0h,

Bits [13] = 1 // Select 100Mbps speed 

Bit [12] = 0 // Disable auto-negotiation 

Bit [8] = 1 // Select full-duplex mode

Or just auto-negotiate and link up at 100BASE-TX full-duplex mode with the link partner.

2. Set Register 1Fh, 

Bit [2] = 1 // Enable remote loopback mode

FIGURE 3-8: REMOTE (ANALOG) LOOPBACK

 

RJ-45

RJ-45

CAT-5
(UTP)

KSZ8081RNA/RND

100BASE-TX
LINK PARTNER

AFE
(ANALOG)

PCS
(DIGITAL)

RMII
DS00002199A-page 20   2016 Microchip Technology Inc.



KSZ8081RNA/RND

3.8 LinkMD® Cable Diagnostic
The LinkMD function uses time-domain reflectometry (TDR) to analyze the cabling plant for common cabling problems.
These include open circuits, short circuits, and impedance mismatches.

LinkMD works by sending a pulse of known amplitude and duration down the MDI or MDI-X pair, then analyzing the
shape of the reflected signal to determine the type of fault. The time duration for the reflected signal to return provides
the approximate distance to the cabling fault. The LinkMD function processes this TDR information and presents it as
a numerical value that can be translated to a cable distance.

LinkMD is initiated by accessing Register 1Dh, the LinkMD Control/Status register, in conjunction with Register 1Fh, the
PHY Control 2 register. The latter register is used to disable Auto MDI/MDI-X and to select either MDI or MDI-X as the
cable differential pair for testing.

3.8.1 USAGE
The following is a sample procedure for using LinkMD with Registers 1Dh and 1Fh:

1. Disable auto MDI/MDI-X by writing a ‘1’ to Register 1Fh, bit [13].
2. Start cable diagnostic test by writing a ‘1’ to Register 1Dh, bit [15]. This enable bit is self-clearing.
3. Wait (poll) for Register 1Dh, bit [15] to return a ‘0’, and indicating cable diagnostic test is completed.
4. Read cable diagnostic test results in Register 1Dh, bits [14:13]. The results are as follows:

00 = normal condition (valid test)

01 = open condition detected in cable (valid test)

10 = short condition detected in cable (valid test)

11 = cable diagnostic test failed (invalid test)

The ‘11’ case, invalid test, occurs when the device is unable to shut down the link partner. In this instance, the test is
not run, since it would be impossible for the device to determine if the detected signal is a reflection of the signal gen-
erated or a signal from another source.

5. Get distance to fault by concatenating Register 1Dh, bits [8:0] and multiplying the result by a constant of 0.38.
The distance to the cable fault can be determined by the following formula:

EQUATION 3-1:

Concatenated value of Registers 1Dh bits [8:0] should be converted to decimal before multiplying by 0.38.

The constant (0.38) may be calibrated for different cabling conditions, including cables with a velocity of propagation
that varies significantly from the norm.

3.9 NAND Tree Support
The KSZ8081RNA/RND provides parametric NAND tree support for fault detection between chip I/Os and board. The
NAND tree is a chain of nested NAND gates in which each KSZ8081RNA/RND digital I/O (NAND tree input) pin is an
input to one NAND gate along the chain. At the end of the chain, the TXD1 pin provides the output for the nested NAND
gates.

The NAND tree test process includes:

• Enabling NAND tree mode
• Pulling all NAND tree input pins high
• Driving each NAND tree input pin low, sequentially, according to the NAND tree pin order
• Checking the NAND tree output to make sure there is a toggle high-to-low or low-to-high for each NAND tree input 

driven low

Table 3-5 lists the NAND tree pin order.

D Dis cetan·  to cable fault in meters  0.38 Register 1Dh, bits[8:0] =
 2016 Microchip Technology Inc.  DS00002199A-page 21



KSZ8081RNA/RND
3.9.1 NAND TREE I/O TESTING
Use the following procedure to check for faults on the KSZ8081RNA/RND digital I/O pin connections to the board:

1. Enable NAND tree mode by setting Register 16h, Bit [5] to ‘1’.
2. Use board logic to drive all KSZ8081RNA/RND NAND tree input pins high.
3. Use board logic to drive each NAND tree input pin, in KSZ8081RNA/RND tree pin order, as follows:

a) Toggle the first pin (MDIO) from high to low, and verify that the TDX1 pin switches from high to low to indicate
that the first pin is connected properly.

b) Leave the first pin (MDIO) low.
c) Toggle the second pin (MDC) from high to low, and verify that the TXD1 pin switches from low to high to

indicate that the second pin is connected properly.
d) Leave the first pin (MDIO) and the second pin (MDC) low.
e) Toggle the third pin from high to low, and verify that the TXD1 pin switches from high-to-low to indicate that

the third pin is connected properly.
f) Continue with this sequence until all KSZ8081RNA/RND NAND tree input pins have been toggled.

Each KSZ8081RNA/RND NAND tree input pin must cause the TXD1 output pin to toggle high-to-low or low-to-high to
indicate a good connection. If the TXD1 pin fails to toggle when the KSZ8081RNA/RND input pin toggles from high to
low, the input pin has a fault.

3.10 Power Management
The KSZ8081RNA/RND incorporates a number of power-management modes and features that provide methods to
consume less energy. These are discussed in the following sections.

3.10.1 POWER-SAVING MODE
Power-saving mode is used to reduce the transceiver power consumption when the cable is unplugged. It is enabled
by writing a ‘1’ to Register 1Fh, Bit [10], and is in effect when auto-negotiation mode is enabled and the cable is discon-
nected (no link). 

In this mode, the KSZ8081RNA/RND shuts down all transceiver blocks except the transmitter, energy detect, and PLL
circuits. 

By default, power-saving mode is disabled after power-up.

3.10.2 ENERGY-DETECT POWER-DOWN MODE
Energy-detect power-down (EDPD) mode is used to further reduce transceiver power consumption when the cable is
unplugged. It is enabled by writing a ‘0’ to Register 18h, Bit [11], and is in effect when auto-negotiation mode is enabled
and the cable is disconnected (no link). 

EDPD mode works with the PLL off (set by writing a ‘1’ to Register 10h, Bit [4] to automatically turn the PLL off in EDPD
mode) to turn off all KSZ8081RNA/RND transceiver blocks except the transmitter and energy-detect circuits.

TABLE 3-5: NAND TREE TEST PIN ORDER FOR KSZ8081RNA/RND
Pin Number Pin Name NAND Tree Description

10 MDIO Input
11 MDC Input
12 RXD1 Input
13 RXD0 Input
15 CRS_DV Input
16 REF_CLK Input
18 INTRP Input
19 TXEN Input
23 LED0 Input
20 TXD0 Input
21 TXD1 Output
DS00002199A-page 22   2016 Microchip Technology Inc.



KSZ8081RNA/RND

Power can be reduced further by extending the time interval between transmissions of link pulses to check for the pres-
ence of a link partner. The periodic transmission of link pulses is needed to ensure two link partners in the same low
power state and with auto MDI/MDI-X disabled can wake up when the cable is connected between them.

By default, energy-detect power-down mode is disabled after power-up.

3.10.3 POWER-DOWN MODE
Power-down mode is used to power down the KSZ8081RNA/RND device when it is not in use after power-up. It is
enabled by writing a ‘1’ to Register 0h, Bit [11]. 

In this mode, the KSZ8081RNA/RND disables all internal functions except the MII management interface. The
KSZ8081RNA/RND exits (disables) power-down mode after Register 0h, Bit [11] is set back to ‘0’.

3.10.4 SLOW-OSCILLATOR MODE
Slow-oscillator mode is used to disconnect the input reference crystal/clock on XI (Pin 8) and select the on-chip slow
oscillator when the KSZ8081RNA/RND device is not in use after power-up. It is enabled by writing a ‘1’ to Register 11h,
Bit[5].

Slow-oscillator mode works in conjunction with power-down mode to put the KSZ8081RNA/RND device in the lowest
power state, with all internal functions disabled except the MII management interface. To properly exit this mode and
return to normal PHY operation, use the following programming sequence:

1. Disable slow-oscillator mode by writing a ‘0’ to Register 11h, Bit [5].
2. Disable power-down mode by writing a ‘0’ to Register 0h, Bit [11].
3. Initiate software reset by writing a ‘1’ to Register 0h, Bit [15].

3.11 Reference Circuit for Power and Ground Connections
The KSZ8081RNA/RND is a single 3.3V supply device with a built-in regulator to supply the 1.2V core. The power and
ground connections are shown in Figure 3-9 and Table 3-6 for 3.3V VDDIO.

FIGURE 3-9: KSZ8081RNA/RND POWER AND GROUND CONNECTIONS

VDDIO

KSZ8081RNA/RND

GND

3.3V

VDDA_3.3

0.1μF
1

VDD_1.2

2

FERRITE
BEAD

14

22 PADDLE

2.2μF

0.1μF22μF

0.1μF22μF
 2016 Microchip Technology Inc.  DS00002199A-page 23



KSZ8081RNA/RND
3.12 Typical Current/Power Consumption
Table 3-7, Table 3-8, and Table 3-9 show typical values for current consumption by the transceiver (VDDA_3.3) and dig-
ital I/O (VDDIO) power pins and typical values for power consumption by the KSZ8081RNA/RND device for the indi-
cated nominal operating voltage combinations. These current and power consumption values include the transmit driver
current and on-chip regulator current for the 1.2V core.

TABLE 3-6: KSZ8081RNA/RND POWER PIN DESCRIPTION
Power Pin Pin Number Description

VDD_1.2 1 Decouple with 2.2 µF and 0.1 µF capacitors to ground.
VDDA_3.3 2 Connect to board’s 3.3V supply through a ferrite bead. Decouple with 

22 µF and 0.1 µF capacitors to ground.
VDDIO 14 Connect to board’s 3.3V supply for 3.3V VDDIO. Decouple with 22 µF 

and 0.1 µF capacitors to ground.

TABLE 3-7: TYPICAL CURRENT/POWER CONSUMPTION (VDDA_3.3 = 3.3V, VDDIO = 3.3V)

Condition 3.3V Transceiver(VDDA_3.3)
3.3V Digital I/Os

(VDDIO) Total Chip Power

100BASE-TX Link-up (no traffic) 34 mA 12 mA 152 mW
100BASE-TX Full-duplex @ 100% utilization 34 mA 13 mA 155 mW

10BASE-T Link-up (no traffic) 14 mA 11 mA 82.5 mW
10BASE-T Full-duplex @ 100% utilization 30 mA 11 mA 135 mW

Power-saving mode (Reg. 1Fh, Bit [10] = 1) 14 mA 10 mA 79.2 mW
EDPD mode (Reg. 18h, Bit [11] = 0) 10 mA 10 mA 66 mW

EDPD mode (Reg. 18h, Bit [11] = 0) and
PLL off (Reg. 10h, Bit [4] = 1)

3.77 mA 1.54 mA 1.75 mW

Software power-down mode (Reg. 0h, Bit [11] =1) 2.59 mA 1.51 mA 13.5 mW
Software power-down mode (Reg. 0h, Bit [11] =1) 

and slow-oscillator mode (Reg. 11h, Bit [5] =1)
1.36 mA 0.45 mA 5.97 mW

TABLE 3-8: TYPICAL CURRENT/POWER CONSUMPTION (VDDA_3.3 = 3.3V, VDDIO = 2.5V)

Condition 3.3V Transceiver(VDDA_3.3)
2.5V Digital I/Os

(VDDIO) Total Chip Power

100BASE-TX Link-up (no traffic) 34 mA 12 mA 142 mW
100BASE-TX Full-duplex @ 100% utilization 34 mA 13 mA 145 mW

10BASE-T Link-up (no traffic) 15 mA 11 mA 77 mW
10BASE-T Full-duplex @ 100% utilization 27 mA 11 mA 117 mW

Power-saving mode (Reg. 1Fh, Bit [10] = 1) 15 mA 10 mA 74.5 mW
EDPD mode (Reg. 18h, Bit [11] = 0) 11 mA 10 mA 61.3 mW

EDPD mode (Reg. 18h, Bit [11] = 0) and
PLL off (Reg. 10h, Bit [4] = 1)

3.55 mA 1.35 mA 15.1 mW

Software power-down mode (Reg. 0h, Bit [11] =1) 2.29 mA 1.34 mA 10.9 mW
Software power-down mode (Reg. 0h, Bit [11] =1) 

and slow-oscillator mode (Reg. 11h, Bit [5] =1)
1.15 mA 0.29 mA 4.52 mW
DS00002199A-page 24   2016 Microchip Technology Inc.



KSZ8081RNA/RND
TABLE 3-9: TYPICAL CURRENT/POWER CONSUMPTION (VDDA_3.3 = 3.3V, VDDIO = 1.8V)

Condition 3.3V Transceiver(VDDA_3.3)
1.8V Digital I/Os

(VDDIO) Total Chip Power

100BASE-TX Link-up (no traffic) 34 mA 11 mA 132 mW
100BASE-TX Full-duplex @ 100% utilization 34 mA 12 mA 134 mW

10BASE-T Link-up (no traffic) 15 mA 10 mA 67.5 mW
10BASE-T Full-duplex @ 100% utilization 27 mA 10 mA 107 mW

Power-saving mode (Reg. 1Fh, Bit [10] = 1) 15 mA 9 mA 65.7 mW
EDPD mode (Reg. 18h, Bit [11] = 0) 11 mA 9 mA 52.5 mW

EDPD mode (Reg. 18h, Bit [11] = 0) and
PLL off (Reg. 10h, Bit [4] = 1)

4.05 mA 1.21 mA 15.5 mW

Software power-down mode (Reg. 0h, Bit [11] =1) 2.79 mA 1.21 mA 11.4 mW
Software power-down mode (Reg. 0h, Bit [11] =1) 

and slow-oscillator mode (Reg. 11h, Bit [5] =1)
1.65 mA 0.19 mA 5.79 mW
 2016 Microchip Technology Inc.  DS00002199A-page 25



KSZ8081RNA/RND
4.0 REGISTER DESCRIPTIONS
This chapter describes the various control and status registers (CSRs).

4.1 Register Map

4.2 Register Descriptions

TABLE 4-1: REGISTERS SUPPORTED BY KSZ8081RNA/RND
Register Number (hex) Description

0h Basic Control
1h Basic Status
2h PHY Identifier 1
3h PHY Identifier 2
4h Auto-Negotiation Advertisement
5h Auto-Negotiation Link Partner Ability
6h Auto-Negotiation Expansion
7h Auto-Negotiation Next Page
8h Link Partner Next Page Ability
9h Reserved

10h Digital Reserved Control
11h AFE Control 1

12h - 14h Reserved
15h RXER Counter
16h Operation Mode Strap Override
17h Operation Mode Strap Status
18h Expanded Control

19h - 1Ah Reserved
1Bh Interrupt Control/Status
1Ch Reserved
1Dh LinkMD Control/Status
1Eh PHY Control 1
1Fh PHY Control 2

TABLE 4-2: REGISTER DESCRIPTIONS

Address Name Description ModeNote 4-1 Default

Register 0h – Basic Control
0.15 Reset 1 = Software reset

0 = Normal operation
This bit is self-cleared after a ‘1’ is written to it.

RW/SC 0

0.14 Loopback 1 = Loopback mode
0 = Normal operation

RW 0

0.13 Speed Select 1 = 100Mbps
0 = 10Mbps
This bit is ignored if auto-negotiation is enabled 
(Register 0.12 = 1).

RW Set by the ANEN_-
SPEED strapping pin.
See the Strap-In 
Options - 
KSZ8081RNA/RND 
section for details.
DS00002199A-page 26   2016 Microchip Technology Inc.



KSZ8081RNA/RND
0.12 Auto-Negoti-
ation Enable

1 = Enable auto-negotiation process
0 = Disable auto-negotiation process
If enabled, the auto-negotiation result overrides the 
settings in Registers 0.13 and 0.8.

RW Set by the ANEN_-
SPEED strapping pin.
See the Strap-In 
Options - 
KSZ8081RNA/RND 
section for details.

0.11 Power-Down 1 = Power-down mode
0 = Normal operation
If software reset (Register 0.15) is used to exit 
power-down mode (Register 0.11 = 1), two soft-
ware reset writes (Register 0.15 = 1) are required. 
The first write clears power-down mode; the sec-
ond write resets the chip and re-latches the pin 
strapping pin values.

RW 0

0.10 Isolate 1 = Electrical isolation of PHY from MII
0 = Normal operation

RW 0

0.9 Restart Auto-
Negotiation

1 = Restart auto-negotiation process
0 = Normal operation.
This bit is self-cleared after a ‘1’ is written to it.

RW/SC 0

0.8 Duplex Mode 1 = Full-duplex
0 = Half-duplex

RW 1

0.7 Collision Test 1 = Enable COL test
0 = Disable COL test

RW 0

0.6:0 Reserved Reserved RO 000_0000
Register 1h - Basic Status
1.15 100Base-T4 1 = T4 capable

0 = Not T4 capable
RO 0

1.14 100Base-TX 
Full-Duplex

1 = Capable of 100Mbps full-duplex
0 = Not capable of 100Mbps full-duplex

RO 1

1.13 100Base-TX 
Half-Duplex

1 = Capable of 100Mbps half-duplex
0 = Not capable of 100Mbps half-duplex

RO 1

1.12 10Base-T 
Full-Duplex

1 = Capable of 10Mbps full-duplex
0 = Not capable of 10Mbps full-duplex

RO 1

1.11 10Base-T 
Half-Duplex

1 = Capable of 10Mbps half-duplex
0 = Not capable of 10Mbps half-duplex

RO 1

1.10:7 Reserved Reserved RO 000_0
1.6 No Preamble 1 = Preamble suppression

0 = Normal preamble
RO 1

1.5 Auto-Negoti-
ation Com-
plete

1 = Auto-negotiation process completed
0 = Auto-negotiation process not completed

RO 0

1.4 Remote Fault 1 = Remote fault
0 = No remote fault

RO/LH 0

1.3 Auto-Negoti-
ation Ability

1 = Can perform auto-negotiation
0 = Cannot perform auto-negotiation

RO 1

1.2 Link Status 1 = Link is up
0 = Link is down

RO/LL 0

1.1 Jabber 
Detect

1 = Jabber detected
0 = Jabber not detected (default is low)

RO/LH 0

TABLE 4-2: REGISTER DESCRIPTIONS (CONTINUED)

Address Name Description ModeNote 4-1 Default
 2016 Microchip Technology Inc.  DS00002199A-page 27



KSZ8081RNA/RND
1.0 Extended 
Capability

1 = Supports extended capability registers RO 1

Register 2h - PHY Identifier 1
2.15:0 PHY ID 

Number
Assigned to the 3rd through 18th bits of the Organi-
zationally Unique Identifier (OUI). KENDIN Com-
munication’s OUI is 0010A1 (hex).

RO 0022h

Register 3h - PHY Identifier 2
3.15:10 PHY ID Num-

ber
Assigned to the 19th through 24th bits of the Orga-
nizationally Unique Identifier (OUI). KENDIN Com-
munication’s OUI is 0010A1 (hex).

RO 0001_01

3.9:4 Model Num-
ber

Six-bit manufacturer’s model number RO 01_0110

3.3:0 Revision 
Number

Four-bit manufacturer’s revision number RO Indicates silicon revi-
sion to Rev. A; A2 = 
0x0, A3 = 0x1.

Register 4h - Auto-Negotiation Advertisement
4.15 Next Page 1 = Next page capable

0 = No next page capability
Note: Recommend to set this bit to ‘0’.

RW 1

4.14 Reserved Reserved RO 0
4.13 Remote Fault 1 = Remote fault supported

0 = No remote fault
RW 0

4.12 Reserved Reserved RO 0
4.11:10 Pause [00] = No pause

[10] = Asymmetric pause
[01] = Symmetric pause
[11] = Asymmetric and symmetric pause

RW 00

4.9 100BASE-T4 1 = T4 capable
0 = No T4 capability

RO 0

4.8 100BASE-TX 
Full-Duplex

1 = 100Mbps full-duplex capable
0 = No 100Mbps full-duplex capability

RW Set by the ANEN_-
SPEED strapping pin.
See the Strap-In 
Options - 
KSZ8081RNA/RND 
section for details.

4.7 100BASE-TX 
Half-Duplex

1 = 100Mbps half-duplex capable
0 = No 100Mbps half-duplex capability

RW Set by the ANEN_-
SPEED strapping pin.
See the Strap-In 
Options - 
KSZ8081RNA/RND 
section for details.

4.6 10BASE-T  
Full-Duplex

1 = 10Mbps full-duplex capable
0 = No 10Mbps full-duplex capability

RW 1

4.5 10BASE-T  
Half-Duplex

1 = 10Mbps half-duplex capable
0 = No 10Mbps half-duplex capability

RW 1

4.4:0 Selector 
Field

[00001] = IEEE 802.3  RW 0_0001

Register 5h - Auto-Negotiation Link Partner Ability
5.15 Next Page 1 = Next page capable

0 = No next page capability
RO 0

TABLE 4-2: REGISTER DESCRIPTIONS (CONTINUED)

Address Name Description ModeNote 4-1 Default
DS00002199A-page 28   2016 Microchip Technology Inc.



KSZ8081RNA/RND
5.14 Acknowledge 1 = Link code word received from partner
0 = Link code word not yet received

RO 0

5.13 Remote Fault 1 = Remote fault detected
0 = No remote fault

RO 0

5.12 Reserved Reserved RO 0
5.11:10 Pause [00] = No pause

[10] = Asymmetric pause
[01] = Symmetric pause
[11] = Asymmetric and symmetric pause

RO 00

5.9 100Base-T4 1 = T4 capable
0 = No T4 capability

RO 0

5.8 100Base-TX 
Full-Duplex

1 = 100Mbps full-duplex capable
0 = No 100Mbps full-duplex capability

RO 0

5.7 100Base-TX 
Half-Duplex

1 = 100Mbps half-duplex capable
0 = No 100Mbps half-duplex capability

RO 0

5.6 10Base-T 
Full-Duplex

1 = 10Mbps full-duplex capable
0 = No 10Mbps full-duplex capability

RO 0

5.5 10Base-T 
Half-Duplex

1 = 10Mbps half-duplex capable
0 = No 10Mbps half-duplex capability

RO 0

5.4:0 Selector 
Field

[00001] = IEEE 802.3  RO 0_0001

Register 6h - Auto-Negotiation Expansion
6.15:5 Reserved Reserved RO 0000_0000_000
6.4 Parallel 

Detection 
Fault

1 = Fault detected by parallel detection
0 = No fault detected by parallel detection

RO/LH 0

6.3 Link Partner 
Next Page 
Able

1 = Link partner has next page capability
0 = Link partner does not have next page capability

RO 0

6.2 Next Page 
Able

1 = Local device has next page capability
0 = Local device does not have next page capabil-
ity

RO 1

6.1 Page 
Received

1 = New page received
0 = New page not received yet

RO/LH 0

6.0 Link Partner 
Auto-Negoti-
ation Able

1 = Link partner has auto-negotiation capability
0 = Link partner does not have auto-negotiation 
capability

RO 0

Register 7h - Auto-Negotiation Next Page
7.15 Next Page 1 = Additional next pages will follow

0 = Last page
RW 0

7.14 Reserved Reserved RO 0
7.13 Message 

Page
1 = Message page
0 = Unformatted page

RW 1

7.12 Acknowl-
edge2

1 = Will comply with message
0 = Cannot comply with message

RW 0

7.11 Toggle 1 = Previous value of the transmitted link code 
word equaled logic 1
0 = Logic 0

RO 0

TABLE 4-2: REGISTER DESCRIPTIONS (CONTINUED)

Address Name Description ModeNote 4-1 Default
 2016 Microchip Technology Inc.  DS00002199A-page 29



KSZ8081RNA/RND
7.10:0 Message 
Field

11-bit wide field to encode 2048 messages RW 000_0000_0001

Register 8h - Link Partner Next Page Ability
8.15 Next Page 1 = Additional next pages will follow

0 = Last page
RO 0

8.14 Acknowledge 1 = Successful receipt of link word
0 = No successful receipt of link word

RO 0

8.13 Message 
Page

1 = Message page
0 = Unformatted page

RO 0

8.12 Acknowl-
edge2

1 = Can act on the information
0 = Cannot act on the information

RO 0

8.11 Toggle 1 = Previous value of transmitted link code word 
equal to logic 0
0 = Previous value of transmitted link code word 
equal to logic 1

RO 0

8.10:0 Message 
Field

11-bit wide field to encode 2048 messages RO 000_0000_0000

Register 10h – Digital Reserved Control
10.15:5 Reserved Reserved RW 0000_0000_000
10.4 PLL Off 1 = Turn PLL off automatically in EDPD mode

0 = Keep PLL on in EDPD mode.
See also Register 18h, Bit [11] for EDPD mode

RW 0

10.3:0 Reserved Reserved RW 0000
Register 11h – AFE Control 1
11.15:6 Reserved Reserved RW 0000_0000_00
11.5 Slow-Oscilla-

tor Mode 
Enable

Slow-oscillator mode is used to disconnect the 
input reference crystal/clock on the XI pin and 
select the on-chip slow oscillator when the 
KSZ8081RNA/RND device is not in use after 
power-up.
1 = Enable
0 = Disable
This bit automatically sets software power-down to 
the analog side when enabled.

RW 0

11.4:0 Reserved Reserved RW 0_0000
Register 15h – RXER Counter
15.15:0 RXER 

Counter
Receive error counter for symbol error frames RO/SC 0000h

Register 16h – Operation Mode Strap Override
16.15 Reserved 

Factory 
Mode

0 = Normal operation
1 = Factory test mode
If RXER (Pin 17) latches in a pull-up value at the 
de-assertion of reset, write a ‘0’ to this bit to clear 
Reserved Factory Mode.

RW 0
Set by the pull-up / 
pull-down value of 
RXER (Pin 17).

16.14:11 Reserved Reserved RW 000_0
16.10 Reserved Reserved RO 0
16.9 B-

CAST_OFF 
Override

1 = Override strap-in for B-CAST_OFF
If bit is ‘1’, PHY Address 0 is non-broadcast.

RW 0

TABLE 4-2: REGISTER DESCRIPTIONS (CONTINUED)

Address Name Description ModeNote 4-1 Default
DS00002199A-page 30   2016 Microchip Technology Inc.



KSZ8081RNA/RND
16.8:7 Reserved Reserved RW 0_0
16.6 RMII B-to-B 

Override
1 = Override strap-in for RMII back-to-back mode 
(also set Bit 1 of this register to ‘1’)

RW 0

16.5 NAND Tree 
Override

1 = Override strap-in for NAND tree mode RW 0

16.4:2 Reserved Reserved RW 0_00
16.1 RMII Over-

ride
1 = Override strap-in for RMII mode RW 1

16.0 Reserved Reserved RW 0
Register 17h - Operation Mode Strap Status
17.15:13 PHYAD[2:0] 

Strap-In Sta-
tus

[000] = Strap to PHY Address 0
[011] = Strap to PHY Address 3
The KSZ8081RNA/RND supports only PHY 
addresses 0h and 3h.

RO

17.12:2 Reserved Reserved RO
17.1 RMII Strap-In 

Status
1 = Strap to RMII mode RO

17.0 Reserved Reserved RO
Register 18h - Expanded Control
18.15:12 Reserved Reserved RW 0000
18.11 EDPD Dis-

abled
Energy-detect power-down mode
1 = Disable
0 = Enable
See also Register 10h, Bit [4] for PLL off.

RW 1

18.10:0 Reserved Reserved RW 000_0000_0000
Register 1Bh – Interrupt Control/Status
1B.15 Jabber Inter-

rupt Enable
1 = Enable jabber interrupt
0 = Disable jabber interrupt

RW 0

1B.14 Receive 
Error Inter-
rupt Enable

1 = Enable receive error interrupt
0 = Disable receive error interrupt

RW 0

1B.13 Page 
Received 
Interrupt 
Enable

1 = Enable page received interrupt
0 = Disable page received interrupt

RW 0

1B.12 Parallel 
Detect Fault 
Interrupt 
Enable

1 = Enable parallel detect fault interrupt
0 = Disable parallel detect fault interrupt

RW 0

1B.11 Link Partner 
Acknowl-
edge Inter-
rupt Enable

1 = Enable link partner acknowledge interrupt
0 = Disable link partner acknowledge interrupt

RW 0

1B.10 Link-Down 
Interrupt 
Enable

1= Enable link-down interrupt
0 = Disable link-down interrupt

RW 0

1B.9 Remote Fault 
Interrupt 
Enable

1 = Enable remote fault interrupt
0 = Disable remote fault interrupt

RW 0

TABLE 4-2: REGISTER DESCRIPTIONS (CONTINUED)

Address Name Description ModeNote 4-1 Default
 2016 Microchip Technology Inc.  DS00002199A-page 31



KSZ8081RNA/RND
1B.8 Link-Up 
Interrupt 
Enable

1 = Enable link-up interrupt
0 = Disable link-up interrupt

RW 0

1B.7 Jabber Inter-
rupt

1 = Jabber occurred
0 = Jabber did not occur

RO/SC 0

1B.6 Receive 
Error Inter-
rupt

1 = Receive error occurred
0 = Receive error did not occur

RO/SC 0

1B.5 Page 
Receive 
Interrupt

1 = Page receive occurred
0 = Page receive did not occur

RO/SC 0

1B.4 Parallel 
Detect Fault 
Interrupt

1 = Parallel detect fault occurred
0 = Parallel detect fault did not occur

RO/SC 0

1B.3 Link Partner 
Acknowl-
edge Inter-
rupt

1 = Link partner acknowledge occurred
0 = Link partner acknowledge did not occur

RO/SC 0

1B.2 Link-Down 
Interrupt

1 = Link-down occurred
0 = Link-down did not occur

RO/SC 0

1B.1 Remote Fault 
Interrupt

1 = Remote fault occurred
0 = Remote fault did not occur

RO/SC 0

1B.0 Link-Up 
Interrupt

1 = Link-up occurred
0 = Link-up did not occur

RO/SC 0

Register 1Dh – LinkMD Control/Status
1D.15 Cable Diag-

nostic Test 
Enable

1 = Enable cable diagnostic test. After test has 
completed, this bit is self-cleared.
0 = Indicates cable diagnostic test (if enabled) has 
completed and the status information is valid for 
read.

RW/SC 0

1D.14:13 Cable Diag-
nostic Test 
Result

[00] = Normal condition
[01] = Open condition has been detected in cable
[10] = Short condition has been detected in cable
[11] = Cable diagnostic test has failed

RO 00

1D.12 Short Cable 
Indicator

1 = Short cable (<10 meter) has been detected by 
LinkMD

RO 0

1D.11:9 Reserved Reserved RW 000
1D.8:0 Cable Fault 

Counter
Distance to fault RO 0_0000_0000

Register 1Eh – PHY Control 1
1E.15:10 Reserved Reserved RO 0000_00
1E.9 Enable 

Pause (Flow 
Control)

1 = Flow control capable
0 = No flow control capability

RO 0

1E.8 Link Status 1 = Link is up
0 = Link is down

RO 0

1E.7 Polarity Sta-
tus

1 = Polarity is reversed
0 = Polarity is not reversed

RO

1E.6 Reserved Reserved RO 0

TABLE 4-2: REGISTER DESCRIPTIONS (CONTINUED)

Address Name Description ModeNote 4-1 Default
DS00002199A-page 32   2016 Microchip Technology Inc.



KSZ8081RNA/RND
1E.5 MDI/MDI-X 
State

1 = MDI-X
0 = MDI

RO

1E.4 Energy 
Detect

1 = Signal present on receive differential pair
0 = No signal detected on receive differential pair

RO 0

1E.3 PHY Isolate 1 = PHY in isolate mode
0 = PHY in normal operation

RW 0

1E.2:0 Operation 
Mode Indica-
tion

[000] = Still in auto-negotiation
[001] = 10Base-T half-duplex
[010] = 100Base-TX half-duplex
[011] = Reserved
[100] = Reserved
[101] = 10Base-T full-duplex
[110] = 100Base-TX full-duplex
[111] = Reserved

RO 000

Register 1Fh – PHY Control 2
1F.15 HP_MDIX 1 = HP Auto MDI/MDI-X mode

0 = Microchip Auto MDI/MDI-X mode
RW 1

1F.14 MDI/MDI-X 
Select

When Auto MDI/MDI-X is disabled,
1 = MDI-X mode
Transmit on RXP,RXM (Pins 4, 3) and Receive on 
TXP,TXM (Pins 6, 5)
0 = MDI mode
Transmit on TXP,TXM (Pins 6, 5) and Receive on 
RXP,RXM (Pins 4, 3)

RW 0

1F.13 Pair Swap 
Disable

1 = Disable Auto MDI/MDI-X
0 = Enable Auto MDI/MDI-X

RW 0

1F.12 Reserved Reserved RW 0
1F.11 Force Link 1 = Force link pass

0 = Normal link operation
This bit bypasses the control logic and allows the 
transmitter to send a pattern even if there is no link.

RW 0

1F.10 Power Sav-
ing

1 = Enable power saving 
0 = Disable power saving

RW 0

1F.9 Interrupt 
Level

1 = Interrupt pin active high
0 = Interrupt pin active low

RW 0

1F.8 Enable Jab-
ber

1 = Enable jabber counter
0 = Disable jabber counter

RW 1

1F.7 RMII Refer-
ence Clock 
Select

1 = For KSZ8081RNA, clock input to XI (Pin 8) is 
50MHz for RMII – 50MHz clock mode.
For KSZ8081RND, clock input to XI (Pin 8) is 
25MHz for RMII – 25MHz clock code.
0 = For KSZ8081RNA, clock input to XI (Pin 8) is 
25MHz for RMII – 25MHz clock code.
For KSZ8081RND, clock input to XI (Pin 8) is 
50MHz for RMII – 50MHz clock mode.

RW 0

1F.6 Reserved Reserved RW 0
1F.5:4 LED Mode [00] = LED0: Link/Activity

[01] = LED0: Link
[10], [11] = Reserved

RW 00

1F.3 Disable 
Transmitter

1 = Disable transmitter
0 = Enable transmitter

RW 0

TABLE 4-2: REGISTER DESCRIPTIONS (CONTINUED)

Address Name Description ModeNote 4-1 Default
 2016 Microchip Technology Inc.  DS00002199A-page 33



KSZ8081RNA/RND
Note 4-1 RW = Read/Write; RO = Read Only; SC = Self-Cleared; LH = Latch High; LL = Latch Low.

1F.2 Remote 
Loopback

1 = Remote (analog) loopback is enabled
0 = Normal mode

RW 0

1F.1 Reserved Reserved RW 0
1F.0 Disable Data 

Scrambling
1 = Disable scrambler
0 = Enable scrambler

RW 0

TABLE 4-2: REGISTER DESCRIPTIONS (CONTINUED)

Address Name Description ModeNote 4-1 Default
DS00002199A-page 34   2016 Microchip Technology Inc.



KSZ8081RNA/RND
5.0 OPERATIONAL CHARACTERISTICS

5.1 Absolute Maximum Ratings*
Supply Voltage (VIN)
(VDD_1.2).................................................................................................................................................... –0.5V to +1.8V

(VDDIO, VDDA_3.3) ...................................................................................................................................... –0.5V to +5.0V

Input Voltage (all inputs)............................................................................................................................ –0.5V to +5.0V

Output Voltage (all outputs)....................................................................................................................... –0.5V to +5.0V

Lead Temperature (soldering, 10s) ....................................................................................................................... +260°C

Storage Temperature (TS) ...................................................................................................................... –55°C to +150°C

*Exceeding the absolute maximum rating may damage the device. Stresses greater than the absolute maximum rating
may cause permanent damage to the device. Operation of the device at these or any other conditions above those spec-
ified in the operating sections of this specification is not implied. Maximum conditions for extended periods may affect
reliability.

5.2 Operating Ratings**
Supply Voltage 

(VDDIO_3.3, VDDA_3.3) ........................................................................................................................ +3.135V to +3.465V

(VDDIO_2.5) ........................................................................................................................................ +2.375V to +2.625V

(VDDIO_1.8) ........................................................................................................................................ +1.710V to +1.890V

Ambient Temperature

(TA Commercial)........................................................................................................................................... 0°C to +70°C

(TA Industrial) ........................................................................................................................................... –40°C to +85°C

Maximum Junction Temperature (TJ max.) ........................................................................................................... +125°C

Thermal Resistance (ΘJA)..............................................................................................................................+47.84°C/W

Thermal Resistance (ΘJC) .............................................................................................................................+14.71°C/W

**The device is not guaranteed to function outside its operating ratings.

Note: Do not drive input signals without power supplied to the device.
 2016 Microchip Technology Inc.  DS00002199A-page 35



KSZ8081RNA/RND
6.0 ELECTRICAL CHARACTERISTICS
TA = 25°C. Specification is for packaged product only.

TABLE 6-1: ELECTRICAL CHARACTERISTICS
Parameters Symbol Min. Typ. Max. Units Note

Supply Current (VDDIO, VDDA_3.3 = 3.3V), Note 6-1
10BASE-T IDD1_3.3V — 41 — mA Full-duplex traffic @ 100% utilization

100BASE-TX IDD2_3.3V — 47 — mA Full-duplex traffic @ 100% utilization

EDPD Mode IDD3_3.3V — 20 — mA
Ethernet cable disconnected 

(Reg. 18h.11 = 0)

Power-Down Mode IDD4_3.3V — 4 — mA
Software power-down 

(Reg. 0h.11 = 1)
CMOS Level Inputs

Output High Voltage VOH

2.4 — — V VDDIO = 3.3V
2.0 — — V VDDIO = 2.5V
1.5 — — V VDDIO = 1.8V

Output Low Voltage VOL

— — 0.4 V VDDIO = 3.3V
— — 0.4 V VDDIO = 2.5V
— — 0.3 V VDDIO = 1.8V

Output Tri-State Leakage |IOZ| — — 10 µA —
LED Output

Output Drive Current ILED — 8 — mA LED0 pin
All Pull-Up/Pull-Down Pins (including Strapping Pins)

Internal Pull-Up Resistance pu
30 45 73 kΩ VDDIO = 3.3V
39 61 102 kΩ VDDIO = 2.5V
48 99 178 kΩ VDDIO = 1.8V

Internal Pull-Down 
Resistance pd

26 43 79 kΩ VDDIO = 3.3V
34 59 113 kΩ VDDIO = 2.5V
53 99 200 kΩ VDDIO = 1.8V

100BASE-TX Transmit (measured differentially after 1:1 transformer)
Peak Differential Output 

Voltage VO 0.95 — 1.05 V
100Ω termination across differential 

output

Output Voltage Imbalance VIMB — — 2 %
100Ω termination across differential 

output
Rise/Fall Time tr/tf 3 — 5 ns —

Rise/Fall Time Imbalance — 0 — 0.5 ns —
Duty Cycle Distortion — — — ±0.25 ns —

Overshoot — — — 5 % —
Output Jitter — — 0.7 — ns Peak-to-peak

10BASE-T Transmit (measured differentially after 1:1 transformer)
Peak Differential Output 

Voltage VP 2.2 — 2.8 V
100Ω termination across differential 

output
Jitter Added — — — 3.5 ns Peak-to-peak

Rise/Fall Time tr/tf — 25 — ns —
10BASE-T Receive

Squelch Threshold VSQ — 400 — mV 5 MHz square wave
Transmitter - Drive Setting
Reference Voltage of ISET VSET — 0.65 — V R(ISET) = 6.49 kΩ
DS00002199A-page 36   2016 Microchip Technology Inc.



KSZ8081RNA/RND
Note 6-1 Current consumption is for the single 3.3V supply KSZ8081RNA/RND device only, and includes the
transmit driver current and the 1.2V supply voltage (VDD_1.2) that are supplied by the KSZ8081RNA/
RND.

REF_CLK Output
50 MHz RMII Clock Output 

Jitter — — 300 — ps
Peak-to-peak. Applies only to RMII - 

25 MHz Clock Mode.
100 Mbps Mode - Industrial Applications Parameters

Link Loss Reaction 
(Indication) Time tllr — 4.4 — µs

Link loss detected at receive 
differential inputs to PHY signal 
indication time for each of the 

following:
1. For LED mode 01, Link LED output 

changes from low (link-up) to high 
(link-down).

2. INTRP pin asserts for link-down 
status change.

TABLE 6-1: ELECTRICAL CHARACTERISTICS (CONTINUED)
Parameters Symbol Min. Typ. Max. Units Note
 2016 Microchip Technology Inc.  DS00002199A-page 37



KSZ8081RNA/RND
7.0 TIMING DIAGRAMS

7.1 RMII Timing

FIGURE 7-1: RMII TIMING - DATA RECEIVED FROM RMII

FIGURE 7-2: RMII TIMING - DATA INPUT TO RMII

TABLE 7-1: RMII TIMING PARAMETERS (25 MHZ INPUT TO XI PIN, 50 MHZ OUTPUT FROM 
REF_CLK PIN)

Parameter Description Min. Typ. Max. Units

tCYC Clock cycle — 20 — ns
t1 Setup time 4 — — ns
t2 Hold time 2 — — ns
tOD Output delay 7 10 13 ns

TABLE 7-2: RMII TIMING PARAMETERS (50 MHZ INPUT TO XI PIN)
Parameter Description Min. Typ. Max. Units

tCYC Clock cycle — 20 — ns
t1 Setup time 4 — — ns
t2 Hold time 2 — — ns
tOD Output delay 8 11 13 ns

tCYC

REF_CLK

TXEN
TXD[1:0]

t1
t2

TRANSMIT TIMING

tCYC

REF_CLK

CRS_DV
RXD[1:0]

RXER

tOD

RECEIVE TIMING
DS00002199A-page 38   2016 Microchip Technology Inc.



KSZ8081RNA/RND

7.2 Auto-Negotiation Timing

FIGURE 7-3: AUTO-NEGOTIATION FAST LINK PULSE (FLP) TIMING

TABLE 7-3: AUTO-NEGOTIATION FAST LINK PULSE TIMING PARAMETERS
Parameter Description Min. Typ. Max. Units

tBTB FLP burst to FLP burst 8 16 24 ms
tFLPW FLP burst width — 2 — ms
tPW Clock/Data pulse width — 100 — ns
tCTD Clock pulse to data pulse 55.5 64 69.5 µs
tCTC Clock pulse to clock pulse 111 128 139 µs
— Number of clock/data pulses per FLP burst 17 — 33 —

AUTO -NEGOTIATION
FAST LINK PULSE (FLP) TIMING

tPW

TX+/TX-

CLOCK
PULSE

DATA
PULSE

CLOCK
PULSE

tPW

tCTD

tCTC

tFLPW

tBTB

TX+/TX-

DATA
PULSE

FLP 
BURST

FLP 
BURST
 2016 Microchip Technology Inc.  DS00002199A-page 39



KSZ8081RNA/RND

7.3 MDC/MDIO Timing

FIGURE 7-4: MDC/MDIO TIMING

TABLE 7-4: MDC/MDIO TIMING PARAMETERS
Parameter Description Min. Typ. Max. Units

fc MDC Clock Frequency — 2.5 10 MHz
tP MDC period — 400 — ns
tMD1 MDIO (PHY input) setup to rising edge of MDC 10 — — ns
tMD2 MDIO (PHY input) hold from rising edge of MDC 4 — — ns
tMD3 MDIO (PHY output) delay from rising edge of MDC 5 222 — ns

tMD1

VALID
DATA

MDIO
(PHY INPUT)

VALID
DATA

MDC

tMD2

MDIO
(PHY OUTPUT)

VALID
DATA

tMD3

tP
DS00002199A-page 40   2016 Microchip Technology Inc.



KSZ8081RNA/RND

7.4 Power-Up/Reset Timing
The KSZ8081RNA/RND reset timing requirement is summarized in Figure 7-5 and Table 7-5.

The supply voltage (VDDIO and VDDA_3.3) power-up waveform should be monotonic. The 300 µs minimum rise time is
from 10% to 90%.

For warm reset, the reset (RST#) pin should be asserted low for a minimum of 500 µs. The strap-in pin values are read
and updated at the de-assertion of reset.

After the de-assertion of reset, wait a minimum of 100 µs before starting programming on the MIIM (MDC/MDIO) inter-
face.

FIGURE 7-5: POWER-UP/RESET TIMING

TABLE 7-5: POWER-UP/RESET TIMING PARAMETERS
Parameter Description Min. Typ. Max. Units

tVR Supply voltage (VDDIO, VDDA_3.3) rise time 300 — — µs
tSR Stable supply voltage (VDDIO, VDDA_3.3) to reset 

high
10 — — ms

tCS Configuration setup time 5 — — ns
tCH Configuration hold time 5 — — ns
tRC Reset to strap-in pin output 6 — — ns

SUPPLY
VOLTAGES

RST#

STRAP-IN
VALUE

STRAP-IN /
OUTPUT  PIN

tVR tSR

tCS tCH

tRC
 2016 Microchip Technology Inc.  DS00002199A-page 41



KSZ8081RNA/RND
8.0 RESET CIRCUIT
Figure 8-1 shows a reset circuit recommended for powering up the KSZ8081RNA/RND if reset is triggered by the power
supply.

FIGURE 8-1: RECOMMENDED RESET CIRCUIT

Figure 8-2 shows a reset circuit recommended for applications where reset is driven by another device (for example,
the CPU or an FPGA). The reset out RST_OUT_n from CPU/FPGA provides the warm reset after power up reset. D2
is used if using different VDDIO between the switch and CPU/FPGA, otherwise, the different VDDIO will fight each other.
If different VDDIO have to use in a special case, a low VF (<0.3V) diode is required (for example, Vishay’s BAT54,
MSS1P2L and so on), or a level shifter device can be used too. If Ethernet device and CPU/FPGA use same VDDIO
voltage, D2 can be removed to connect both devices directly. Usually, Ethernet device and CPU/FPGA should use same
VDDIO voltage.

FIGURE 8-2: RECOMMENDED RESET CIRCUIT FOR CPU/FPGA RESET OUTPUT

VDDIO

D1: 1N4148

D1 R 10KKSZ8081RNA/RND

RST#

C 10μF

VDDIO

KSZ8081RNA/RND
D1

R 10K

RST#

C 10μF
D2

CPU/FPGA

RST_OUT_n

D1, D2: 1N4148
DS00002199A-page 42   2016 Microchip Technology Inc.



KSZ8081RNA/RND
9.0 REFERENCE CIRCUITS — LED STRAP-IN PINS
The pull-up, float, and pull-down reference circuits for the LED0/ANEN_SPEED strapping pin are shown in Figure 9-1
for 3.3V and 2.5V VDDIO. 

FIGURE 9-1: REFERENCE CIRCUITS FOR LED STRAPPING PINS

For 1.8V VDDIO, LED indication support is not recommended due to the low voltage. Without the LED indicator, the
ANEN_SPEED strapping pin is functional with a 4.7 kΩ pull-up to 1.8V VDDIO or float for a value of ‘1’, and with a 1.0 kΩ
pull-down to ground for a value of ‘0’.

If using RJ45 jacks with integrated LEDs and 1.8V VDDIO, a level shifting is required from LED 3.3V to 1.8V. For example,
use a bipolar transistor or a level shift device.

 

LED0 PIN

2204.7k
PULL-UP

KSZ8081RNA/RND

VDDIO = 3.3V, 2.5V

 

LED0 PIN

220
FLOAT

KSZ8081RNA/RND

VDDIO = 3.3V, 2.5V

 

LED0 PIN

220
PULL-DOWN

KSZ8081RNA/RND

VDDIO = 3.3V, 2.5V

1k
 2016 Microchip Technology Inc.  DS00002199A-page 43



KSZ8081RNA/RND
10.0 REFERENCE CLOCK - CONNECTION AND SELECTION
A crystal or external clock source, such as an oscillator, is used to provide the reference clock for the KSZ8081RNA/
RND. For the KSZ8081RNA/RND in RMII – 25 MHz clock mode, the reference clock is 25 MHz. The reference clock
connections to XI (Pin 8) and XO (Pin 7), and the reference clock selection criteria, are provided in Figure 10-1 and
Table 10-1.

FIGURE 10-1: 25 MHZ CRYSTAL/OSCILLATOR REFERENCE CLOCK CONNECTION

Note 10-1 ±60 ppm for overtemperature crystal.
For the KSZ8081RNA/RND in RMII – 50 MHz clock mode, the reference clock is 50 MHz. The reference clock connec-
tion to XI (Pin 8), and the reference clock selection criteria are provided in Figure 10-2 and Table 10-2.

FIGURE 10-2: 50 MHZ OSCILLATOR/REFERENCE CLOCK CONNECTION

TABLE 10-1: 25 MHZ CRYSTAL/REFERENCE CLOCK SELECTION CRITERIA
Characteristics Value

Frequency 25 MHz
Frequency Tolerance (max.); Note 10-1 ±50 ppm

Crystal Series Resistance (typ.) 40Ω
Crystal Load Capacitance (typ.) 16 pF

TABLE 10-2: 50 MHZ OSCILLATOR/REFERENCE CLOCK SELECTION CRITERIA
Characteristics Value

Frequency 50 MHz
Frequency Tolerance (max.) ±50 ppm

NC

XI

XO

25MHz OSC
±50ppm

XI

XO

25MHz XTAL
±50ppm

22pF

22pF

NC

XI

XO

50MHz OSC
±50ppm
DS00002199A-page 44   2016 Microchip Technology Inc.



KSZ8081RNA/RND
11.0 MAGNETIC - CONNECTION AND SELECTION
A 1:1 isolation transformer is required at the line interface. Use one with integrated common-mode chokes for designs
exceeding FCC requirements. 

The KSZ8081RNA/RND design incorporates voltage-mode transmit drivers and on-chip terminations. 

With the voltage-mode implementation, the transmit drivers supply the common-mode voltages to the two differential
pairs. Therefore, the two transformer center tap pins on the KSZ8081RNA/RND side should not be connected to any
power supply source on the board; instead, the center tap pins should be separated from one another and connected
through separate 0.1 µF common-mode capacitors to ground. Separation is required because the common-mode volt-
age is different between transmitting and receiving differential pairs.

Figure 11-1 shows the typical magnetic interface circuit for the KSZ8081RNA/RND.

FIGURE 11-1: TYPICAL MAGNETIC INTERFACE CIRCUIT

Table 11-1 lists recommended magnetic characteristics.

Table 11-2 is a list of compatible single-port magnetics with separated transformer center tap pins on the PHY chip side
that can be used with the KSZ8081RNA/RND.

TABLE 11-1: MAGNETICS SELECTION CRITERIA
Parameter Value Test Conditions

Turns Ratio 1 CT : 1 CT —
Open-Circuit Inductance (min.) 350 µH 100 mV, 100 kHz, 8 mA

Insertion Loss (max.) –1.1 dB 100 kHz to 100 MHz
HIPOT (min.) 1500 VRMS —

1

2

3

7

8

4

5

6

4 x 75

1000pF/2kV 

R
J-

45
 C

O
N

N
E

C
TO

R

CHASSIS GROUND

(2 x 0.1μF)

TXP

TXM

RXP

RXM

K
SZ

80
81

R
N

A
/R

N
D

SIGNAL GROUND
 2016 Microchip Technology Inc.  DS00002199A-page 45

 

 

 

 

| em |

 

 
�

KSZ8081RNA/RND
TABLE 11-2: COMPATIBLE SINGLE-PORT 10/100 MAGNETICS
Manufacturer Part Number Temperature Range Magnetic + RJ-45

Bel Fuse S558-5999-U7 0°C to 70°C No
Bel Fuse SI-46001-F 0°C to 70°C Yes
Bel Fuse SI-50170-F 0°C to 70°C Yes

Delta LF8505 0°C to 70°C No
HALO HFJ11-2450E 0°C to 70°C Yes
HALO TG110-E055N5 –40°C to 85°C No

LANKom LF-H41S-1 0°C to 70°C No
Pulse H1102 0°C to 70°C No
Pulse H1260 0°C to 70°C No
Pulse HX1188 –40°C to 85°C No
Pulse J00-0014 0°C to 70°C Yes
Pulse JX0011D21NL –40°C to 85°C Yes
TDK TLA-6T718A 0°C to 70°C Yes

Transpower HB726 0°C to 70°C No
Wurth/Midcom 000-7090-37R-LF1 –40°C to 85°C No
DS00002199A-page 46   2016 Microchip Technology Inc.



 2016 Microchip Technology Inc.  DS00002199A-page 47

KSZ8081RNA/RND

12.0 PACKAGE OUTLINE

Note: For the most current package drawings, please see the Microchip Packaging Specification located at 
http://www.microchip.com/packaging

FIGURE 12-1: 24-LEAD QFN 4 MM X 4 MM PACKAGE

TITLE

24 LEAD QFN 4x4mm PACKAGE OUTLINE & RECOMMENDED LAND PATTERN

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
 

 

 

 

 

 

 

 

 

 

 

 

DRAWING # | QFN44-24LD-PL-1 UNIT | MM
2.504005 PIN #1 ID
Pin 1 Dot — 4.00 BSC — [“t Exp, Dap“)
By marking
1 oaooto0s| UJ Y
2 i Dp —>
3 { ID R020 C] 1
o.25z005[ ca
“ap ase “WD es
D q !
0.500 BSC
i)
FLonannn
@po00
IOP VIEW BOTTOM VIEW
Mare 2, 3 NOTE 1, 2, 3
484002
UOU000 .
o mR
0.850+0.050 _ Ge oe
aJo.os[c ten ooo oo dt + = =
SEATING PLANE {_ y y
0.20340.025 0.0248 g o ot
a | |
SIDE VIEW 5 im in
wre ea °| |MO0000
-——2.6+0,02——
3,2440.0;
200.0
RECOMMENDED LAND PATTERN
NOTE: NOTE: 4,

1, MAX PACKAGE WARPAGE IS 0.05 MM
2, MAX ALLOWABLE BURR IS _0,076MM

IN ALL DIRECTIONS
3, PIN #1 1S ON TOP WILL BE LASER MARKED

4, RED CIRCLE IN LAND PATTERN INDICATE THERMAL VIA. SIZE SHOULD BE 0.30-0.35M IN
DIAMETER AND SHOULD BE CONNECTED TO GND FOR MAX THERMAL PERFORMANCE

5. GREEN RECTANGLES (SHADED AREA) Indicate SOLDER STENCIL OPENING ON EXPOSED PAD
AREA, SIZE SHOULD BE 1,00x1,00 MM IN SIZE, 1.20 MM PITCH,
�

KSZ8081RNA/RND

DS00002199A-page 48   2016 Microchip Technology Inc.

APPENDIX A: DATA SHEET REVISION HISTORY

TABLE A-1: REVISION HISTORY

Revision Section/Figure/Entry Correction

DS00002199A (06-14-16) —
Converted Micrel data sheet KSZ8081RNA/RND to 
Microchip DS00002199A. Minor text changes 
throughout.



 2016 Microchip Technology Inc.  DS00002199A-page 49

KSZ8081RNA/RND

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To register, access the Microchip web site at www.microchip.com. Under “Support”, click on “Customer Change Notifi-
cation” and follow the registration instructions.

CUSTOMER SUPPORT
Users of Microchip products can receive assistance through several channels:

• Distributor or Representative
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Customers should contact their distributor, representative or field application engineer (FAE) for support. Local sales
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Technical support is available through the web site at: http://microchip.com/support

http://www.microchip.com
http://www.microchip.com
http://www.microchip.com


KSZ8081RNA/RND

DS00002199A-page 50   2016 Microchip Technology Inc.

PRODUCT IDENTIFICATION SYSTEM
To order or obtain information, e.g., on pricing or delivery, refer to the factory or the listed sales office.

   
Device: KSZ8081

Interface: R = RMII

Package: N = 24-pin QFN

Special Attribute: A = 25 MHz Input/50 MHz Output Clocks
D = 50 MHz Input Clock

Temperature: CA = 0C to +70C (Commercial)
IA = –40C to +85C (Industrial)

Examples:
a) KSZ8081RNACA

RMII Interface
24-pin QFN
25 MHz Input/50 MHz Output
Commercial Temperature

b) KSZ8081RNAIA
RMII Interface
24-pin QFN
25 MHz Input/50 MHz Output
Industrial Temperature

c) KSZ8081RNDCA
RMII Interface
24-pin QFN
50 MHz Input
Commercial Temperature

d) KSZ8081RNDIA
RMII Interface
24-pin QFN
50 MHz Input
Industrial Temperature

PART NO. X X

PackageInterfaceDevice

X

Temperature

X

Special
Attribute



 2016 Microchip Technology Inc.  DS00002199A-page 51

Information contained in this publication regarding device applications and the like is provided only for your convenience and may be
superseded by updates. It is your responsibility to ensure that your application meets with your specifications. MICROCHIP MAKES NO
REPRESENTATIONS OR WARRANTIES OF ANY KIND WHETHER EXPRESS OR IMPLIED, WRITTEN OR ORAL, STATUTORY OR
OTHERWISE, RELATED TO THE INFORMATION, INCLUDING BUT NOT LIMITED TO ITS CONDITION, QUALITY, PERFORMANCE,
MERCHANTABILITY OR FITNESS FOR PURPOSE. Microchip disclaims all liability arising from this information and its use. Use of Micro-
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harmless Microchip from any and all damages, claims, suits, or expenses resulting from such use. No licenses are conveyed, implicitly or
otherwise, under any Microchip intellectual property rights unless otherwise stated.

Trademarks

The Microchip name and logo, the Microchip logo, AnyRate, dsPIC, FlashFlex, flexPWR, Heldo, JukeBlox, KeeLoq, KeeLoq logo, 
Kleer, LANCheck, LINK MD, MediaLB, MOST, MOST logo, MPLAB, OptoLyzer, PIC, PICSTART, PIC32 logo, RightTouch, SpyNIC, 
SST, SST Logo, SuperFlash and UNI/O are registered trademarks of Microchip Technology Incorporated in the U.S.A. and other 
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ClockWorks, The Embedded Control Solutions Company, ETHERSYNCH, Hyper Speed Control, HyperLight Load, IntelliMOS, 
mTouch, Precision Edge, and QUIET-WIRE are registered trademarks of Microchip Technology Incorporated in the U.S.A.

Analog-for-the-Digital Age, Any Capacitor, AnyIn, AnyOut, BodyCom, chipKIT, chipKIT logo, CodeGuard, dsPICDEM, dsPICDEM.net, 
Dynamic Average Matching, DAM, ECAN, EtherGREEN, In-Circuit Serial Programming, ICSP, Inter-Chip Connectivity, JitterBlocker, 
KleerNet, KleerNet logo, MiWi, motorBench, MPASM, MPF, MPLAB Certified logo, MPLIB, MPLINK, MultiTRAK, NetDetach, 
Omniscient Code Generation, PICDEM, PICDEM.net, PICkit, PICtail, PureSilicon, RightTouch logo, REAL ICE, Ripple Blocker, Serial 
Quad I/O, SQI, SuperSwitcher, SuperSwitcher II, Total Endurance, TSHARC, USBCheck, VariSense, ViewSpan, WiperLock, Wireless 
DNA, and ZENA are trademarks of Microchip Technology Incorporated in the U.S.A. and other countries.

SQTP is a service mark of Microchip Technology Incorporated in the U.S.A.

Silicon Storage Technology is a registered trademark of Microchip Technology Inc. in other countries.

GestIC is a registered trademarks of Microchip Technology Germany II GmbH & Co. KG, a subsidiary of Microchip Technology Inc., in 
other countries. 

All other trademarks mentioned herein are property of their respective companies.

© 2016, Microchip Technology Incorporated, Printed in the U.S.A., All Rights Reserved. 

ISBN: 978-1-5224-0855-0

Note the following details of the code protection feature on Microchip devices:
• Microchip products meet the specification contained in their particular Microchip Data Sheet.

• Microchip believes that its family of products is one of the most secure families of its kind on the market today, when used in the 
intended manner and under normal conditions.

• There are dishonest and possibly illegal methods used to breach the code protection feature. All of these methods, to our 
knowledge, require using the Microchip products in a manner outside the operating specifications contained in Microchip’s Data 
Sheets. Most likely, the person doing so is engaged in theft of intellectual property.

• Microchip is willing to work with the customer who is concerned about the integrity of their code.

• Neither Microchip nor any other semiconductor manufacturer can guarantee the security of their code. Code protection does not 
mean that we are guaranteeing the product as “unbreakable.”

Code protection is constantly evolving. We at Microchip are committed to continuously improving the code protection features of our
products. Attempts to break Microchip’s code protection feature may be a violation of the Digital Millennium Copyright Act. If such acts
allow unauthorized access to your software or other copyrighted work, you may have a right to sue for relief under that Act.

Microchip received ISO/TS-16949:2009 certification for its worldwide 
headquarters, design and wafer fabrication facilities in Chandler and 
Tempe, Arizona; Gresham, Oregon and design centers in California 
and India. The Company’s quality system processes and procedures 
are for its PIC® MCUs and dsPIC® DSCs, KEELOQ® code hopping 
devices, Serial EEPROMs, microperipherals, nonvolatile memory and 
analog products. In addition, Microchip’s quality system for the design 
and manufacture of development systems is ISO 9001:2000 certified.

QUALITY	MANAGEMENT		SYSTEM	
CERTIFIED	BY	DNV	

== ISO/TS	16949	==	



DS00002199A-page 52  2016 Microchip Technology Inc.

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Worldwide Sales and Service

06/23/16

S

MICROCHIP
�http://support.microchip.com
http://www.microchip.com

	1.0 Introduction
	1.1 General Description

	2.0 Pin Description and Configuration
	3.0 Functional Description
	3.1 10BASE-T/100BASE-TX Transceiver
	3.2 RMII Interface
	3.3 Back-to-Back Mode – 100 Mbps Copper Repeater
	3.4 MII Management (MIIM) Interface
	3.5 Interrupt (INTRP)
	3.6 HP Auto MDI/MDI-X
	3.7 Loopback Mode
	3.8 LinkMD® Cable Diagnostic
	3.9 NAND Tree Support
	3.10 Power Management
	3.11 Reference Circuit for Power and Ground Connections
	3.12 Typical Current/Power Consumption

	4.0 Register Descriptions
	4.1 Register Map
	4.2 Register Descriptions

	5.0 Operational Characteristics
	5.1 Absolute Maximum Ratings*
	5.2 Operating Ratings**

	6.0 Electrical Characteristics
	7.0 Timing Diagrams
	7.1 RMII Timing
	7.2 Auto-Negotiation Timing
	7.3 MDC/MDIO Timing
	7.4 Power-Up/Reset Timing

	8.0 Reset Circuit
	9.0 Reference Circuits — LED Strap-In Pins
	10.0 Reference Clock - Connection and Selection
	11.0 Magnetic - Connection and Selection
	12.0 Package Outline
