COM20020 Datasheet, PDF (21/72 Pages) SMSC Corporation – COM20020 3.3V ULANC Universal Local Area Network Controller with 2K x 8 On-Board RAM

The Differential Driver Configuration cannot
communicate directly with nodes utilizing the
Traditional Hybrid Configuration. Like 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 a
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.
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