COM20020_00 Datasheet, PDF (6/82 Pages) SMSC Corporation – Universal Local Area Network Controller with 2K x 8 On-Board RAM

DIP PIN
NO.
21
16,15
17
18
13,14
24
12
PLCC PIN
NO.
NAME
SYMBOL
25
nChip Select nCS
DESCRIPTION
Input. This active low signal selects the
COM20020 for an access.
TRANSMISSION MEDIA INTERFACE
19,18
nPulse 2,
nPulse 1
nPULSE2,
nPULSE1
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.
20
Receive In RXIN
Input. This signal carries the receive data
information from the line tranceiver.
21
nTransmit nTXEN
Output. This signal is used prior to the Power-
nEnable
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)
16,17
Crystal
Oscillator
XTAL1,
XTAL2
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.
15,28
Power
V_DD
Supply
+3.3 Volt Power Supply pin.
7,14,22 Ground
V_SS
Ground pin.
6
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