DIP PIN
NO.
21
PLCC PIN
NO.
NAME
25
nChip Select
SYMBOL
nCS
DESCRIPTION
Input. This active low signal selects the
COM20020 for an access.
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.
Input. This signal carries the receive data
information from the line tranceiver.
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)
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 390Ω pull-up resistor, and XTAL2
should be left floating.
+3.3 Volt Power Supply pin.
Ground pin.
TRANSMISSION MEDIA INTERFACE
16,15
19,18
nPulse 2,
nPulse 1
nPULSE2,
nPULSE1
17
18
20
21
Receive In
nTransmit
nEnable
RXIN
nTXEN
13,14
16,17
Crystal
Oscillator
XTAL1,
XTAL2
24
12
15,28
7,14,22
Power
Supply
Ground
V
DD
V
SS
6
SMSC [ SMSC CORPORATION ]
