COM20020 datasheet(21/72 Pages) SMSC

21 / 72 page

The

Differential

Driver

Configuration

cannot

communicate directly with nodes utilizing the

Traditional

Hybrid

Configuration.

the

Backplane Configuration, the Differential Driver

Configuration does not isolate the node from the

media.

The Differential Driver interface includes a RS485

Driver/Receiver to transfer the data between the

cable and the COM20020. The nPULSE1 signal

transmits the data, provided the Transmit Enable

signal is active.

The nPULSE1 signal issues a

200nS (at 2.5Mbps) negative pulse to transmit a

logic "1". Lack of pulse indicates a logic "0". The

RXIN signal receives the data, the transmitter

portion of the COM20020 is disabled during reset

and the nPULSE1, nPULSE2 and nTXEN pins are

inactive.

Programmable TXEN Polarity

To accommodate transceivers with active high

ENABLE

pins,

the

COM20020

contains

programmable TXEN output.

To program the

TXEN pin for an active high pulse, the nPULSE2

pin should be connected to ground. To retain the

normal active low polarity, nPULSE2 should be

left open. The polarity determination is made at

power on reset and is valid only for Backplane

Mode operation.

The nPULSE2 pin should

remain grounded at all times if an active high

polarity is desired.

COM20020 Datenblatt(PDF) 21 Page - SMSC Corporation

COM20020 Datenblatt(HTML) 21 Page - SMSC Corporation

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