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AM79C940JC

Media Access Controller for Ethernet (MACE™)

Advanced Micro Devices 

TXEN/TXEN

Transmit Enable (Output)

When the AUI port is selected (PORTSEL [1-0] = 00),

an output indicating that the AUI DO± differential output

has valid Manchester encoded data is presented.

When the 10BASE-T port is selected (PORTSEL [1-0]

= 01), indicates that Manchester data is being output

on the TXD±/TXP± complementary outputs. When the

DAI port is selected (PORTSEL [1–0] = 10), indicates

that Manchester data is being output on the DAI port

TXDAT± complementary outputs. When the GPSI port

is selected (PORTSEL [1–0] =11), indicates that NRZ

data is being output from the MAC core of the MACE

device, to an external Manchester encoder/decoder, on

the TXDAT+ output. Active low when the DAI port is

selected, active high when the AUI, 10 BASE-T or

GPSI is selected. Operates at TTL levels.

RXDAT

Receive Data (Input)

When the DAI port is selected (PORTSEL [1–0] = 10),

the Manchester encoded data input to the integrated

clock recovery and Manchester decoder of the MACE

device, from an external network transceiver. When the

GPSI port is selected (PORTSEL [1–0] =11), the NRZ

decoded data input to the MAC core of the MACE

device, from an external Manchester encoder/decoder.

Operates at TTL levels.

RXCRS

Receive Carrier Sense (Input/Output)

When the AUI port is selected (PORTSEL [1–0] = 00),

an output indicating that the DI± input pair is receiving

valid Manchester encoded data from the external

transceiver which meets the signal amplitude and

pulse width requirements. When the 10BASE-T port is

selected (PORTSEL [1–0] = 01), an output indicating

that the RXD± input pair is receiving valid Manchester

encoded data from the twisted pair cable which meets

the signal amplitude and pulse width requirements.

RXCRS will be asserted high for the entire duration of

the receive message. When the DAI port is selected

(PORTSEL [1-0] = 10), an input signaling the MACE

device that a receive carrier condition has been

detected on the network, and valid Manchester

encoded data is being presented to the MACE device

on the RXDAT line. When the GPSI port is selected

(PORTSEL [1-0] = 11), an input signalling the internal

MAC core that valid NRZ data is being presented on

the RXDAT input. Operates at TTL levels.

TXEN/TXEN Configuration

SLEEP

PORTSEL

[1-0]

ENDPLSIO

Interface Description

Pin Function

0

XX

X

Sleep Mode

High Impedance

1

00

1

AUI

TXEN Output

1

01

1

10BASE-T

TXEN Output

1

10

1

DAI Port

TXEN Output

1

11

1

GPSI

TXEN Output

1

XX

0

Status Disabled

High Impedance (Note 3)

Notes:

1. PORTSEL [1–0] and ENPLSIO are located in the PLS Configuration Control register (REG ADDR 14).

2. When the GPSI port is selected, TXEN should have an external pull-down attached (e.g. 3.3k Ω) to ensure the output is held

inactive before ENPLSIO is set.

3. This pin should be externally terminated, if unused, to reduce power consumption.

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Am79C940

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