50 Pin Descriptions

Pin No

Name

IO

Description

(DIP)

(PCC)

1

1

COL

O

Collision Detect Output

A TTLMOS level active high output A 10 MHz

output When no signal is present at the collision input COL output will go low

2

2

RXD

O

Receive Data Output

A TTLMOS level signal This is the NRZ data output

from the digital phase-locked loop This signal should be sampled by the

controller at the rising edge of receive clock

3

3

CRS

O

Carrier Sense

A TTLMOS level active high signal It is asserted when valid

data from the transceiver is present at the receive input It is de-asserted one

and a half bit times after the last bit at receive input

4

4

RXC

O

Receive Clock

A TTLMOS level recovered clock When the phase-locked loop

locks to a valid incoming signal a 10 MHz clock signal is activated on this output

This output remains low during idle (5 bit times after activity ceases at receive

input)

5

5

SEL

I

Mode Select

are at the same voltage in idle state providing a ‘‘zero’’ differential When low

6

6–9

GND

Negative Supply Pins

7

10

LBK

I

Loopback

A TTL level active high on this input enables the loopback mode

811

X1

I

Crystal or External Frequency Source Input (TTL)

912

X2

O

Crystal Feedback Output

This output is used in the crystal connection only It

must be left open when driving X1 with an external frequency source

10

13

TXD

I

Transmit Data

A TTL level input This signal is sampled by the SNI at the rising

edge of transmit clock when transmit enable input is high The SNI combines

transmit data and transmit clock signals into a Manchester encoded bit stream

and sends it differentially to the transceiver

11

14

TXC

O

Transmit Clock

A TTLMOS level 10 MHz clock signal derived from the 20

MHz oscillator This clock signal is always active

12

15

TXE

I

Transmit Enable

A TTL level active high data encoder enable input This signal

is also sampled by the SNI at the rising edge of transmit clock

13

16

O

Transmit Output

Differential line driver which sends the encoded data to the

transceiver These outputs are source followers and require 270X pulldown

14

17

resistors to GND

15

18

NC

No Connection

16

17

19

CAP

O

Bypass Capacitor

A ceramic capacitor (greater than 0001 mF) must be

connected from this pin to GND

18

20 – 23

VCC

Positive Supply Pins

A 01 mF ceramic decoupling capacitor must be

connected across VCC and GND as close to the device as possible

19

20

24

NC

No Connection

21

25

I

Receive Input

Differential receive input pair from the transceiver

22

26

23

27

I

Collision Input

Differential collision input pair from the transceiver

24

28

5