COM20051 datasheet(5/82 Pages) SMSC

5 / 82 page

DESCRIPTION OF PIN FUNCTIONS

PIN NO.

NAME

SYMBOL

DESCRIPTION

nPulse 2

nPULSE2

Output. Network output. Outputs a synchronous

clock at 2x the data rate when backplane mode is

invoked.

24-31

P2.0-2.7

Input/Output. Port 2 of the 8051. High order address

bus.

nProgram Store

Enable

nPSEN

Output.

Address Latch

Enable

ALE

Output.

Transmit Enable TXEN

Output. This signal is used to enable the drivers for

transmitting. The polarity of this signal is

programmable by grounding the nPULSE2 pin prior

to the POWER-UP.

nPULSE2 floating prior to the power-up = TXEN

active high

nPULSE2 grounded prior to the power-up = TXEN

active low. (This option is available only in the

Backplane mode).

nEnable

nEA

Input. When high, causes the 8051's outputs to tri-

state. When low, allows the 8051 to address external

memory. Must be low to execute code from the

embedded 8051.

36-43

P0.7-0.0

Input/Output. Port 0 of the 8051. Multiplexed low

order address/data bus.

Power Supply

VCC

+5V power supply.

RESET CIRCUIT FOR THE COM20051

The power on reset circuit for the COM20051 should be designed to provide a clean, fast transition time

TTL input to the COM20051. Sufficient signal high time on RST (pin 10) should be provided after Vcc

reaches +5V DC. The following circuit, which provides an 8ms power-on reset pulse, is recommended:

Vcc (+5V)

22uF/

10V

RST (PIN 10)

220

74LS14

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