COM20020 Datasheet, PDF (20/72 Pages) SMSC Corporation – COM20020 3.3V ULANC Universal Local Area Network Controller with 2K x 8 On-Board RAM

1
1
0
20MHZ
CLOCK
(FOR REF.
ONLY)
100ns
nPULSE1
100ns
nPULSE2
200ns
DIPULSE
RXIN
400ns
FIGURE 6 - DIPULSE WAVEFORM FOR DATA OF 1-1-0
In typical applications, the serial backplane is
terminated at both ends and a bias is provided by
the external pull-up resistor.
The RXIN signal is directly connected to the cable
via an internal Schmitt trigger. A negative pulse
on this input indicates a logic "1". Lack of pulse
indicates a logic "0". For typical single-ended
backplane applications, RXIN is connected to
nPULSE1 to make the serial backplane data line.
A ground line (from the coax or twisted pair)
should run in parallel with the signal. For
applications requiring different treatment of the
receive signal (like filtering or squelching),
nPULSE1 and RXIN remain as independent pins.
External differential drivers/receivers for increased
range and common mode noise rejection, for
example, would require the signals to be
independent of one another.
When the device is in Backplane Mode, the clock
provided by the nPULSE2 signal may be used for
encoding the data into a different encoding
scheme or other synchronous operations needed
on the serial data stream.
Differential Driver Configuration
The Differential Driver Configuration is a special
case of the Backplane Mode. It is a dc coupled
configuration recommended for applications like
car-area networks or other cost-sensitive
applications which do not require direct
compatibility with existing ARCNET nodes and do
not require isolation.
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