COM20020D datasheet(6/72 Pages) SMSC

6 / 72 page

DIP PIN

NO.

PLCC PIN

NO.

NAME

SYMBOL

DESCRIPTION

TRANSMISSION MEDIA INTERFACE

16,15

19,18

nPulse 2,

nPulse 1

nPULSE2,

nPULSE1

Output (nPULSE1), Input/Output (nPULSE2).

In Normal Mode, these active low signals

carry the transmit data information, encoded

in pulse format, as DIPULSE waveform.

When the device is in Backplane Mode, the

nPULSE1 signal driver is programmable

(push/pull or open-drain), while the nPULSE2

signal provides a clock with frequency of

double the data rate. nPULSE1 is connected

to a weak internal pull-up resistor on the

open/drain driver in backplane mode.

Receive In

RXIN

Input.

This signal carries the receive data

information from the line tranceiver.

nTransmit

nEnable

nTXEN

Output. This signal is used prior to the Power-

up to enable the line drivers for transmission.

The polarity of the signal is programmable

through the nPULSE2 pin.

nPULSE2 floating before Power-up: nTXEN

active low (Default option)

nPULSE2

grounded

before

Power-up:

nTXEN active high (This option is only

available in Backplane Mode)

13,14

16,17

Crystal

Oscillator

XTAL1,

XTAL2

An external crystal should be connected to

these pins.

Oscillation frequency range is

from 10 to 20 MHz. If an external TTL clock is

used instead, it must be connected to XTAL1

with a 390

Ω pull-up resistor, and XTAL2

should be left floating.

15,28

Power

Supply

VDD

+5 Volt Power Supply pin.

7,14,22

Ground

VSS

Ground pin.

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