COM20020-5 Datasheet, PDF (4/58 Pages) SMSC Corporation – Universal Local Area Network Controller with 2K x 8 On-Board RAM

DIP PIN
NO.
1-3
4-11
23
22
DESCRIPTION OF PIN FUNCTIONS
PLCC PIN
NO.
NAME
SYMBOL
DESCRIPTION
MICROCONTROLLER INTERFACE
1-3
Address
A0/nMUX, Input. On a non-multiplexed bus, these
0-2
A1,A2/ALE signals are directly connected to the low bits
of the host address bus. On a multiplexed
address/data bus, A0/nMUX is tied low, A1
is left open, and A2 is tied to the Address
Latch Enable signal of the host. A1 is
connected to an internal pull-up resistor.
4-6,8-12 Data 0-7
AD0-AD2, Input/Output. On a non-multiplexed bus,
D3-D7
these signals are used as the data lines for
the device. On a multiplexed address/data
bus, AD0-AD2 act as the address lines
(latched by ALE) and as the low data lines
for the device. D3-D7 are always used for
data only. These signals are connected to
internal pull-up resistors.
27
nRead/nDat nRD/nDS Input. On a 68XX-like bus, this active low
a
signal is issued by the microcontroller as the
nStrobe
data strobe signal to strobe the data onto
the bus. On a 80XX-like bus, this active low
signal is issued by the microcontroller to
indicate a read operation. In this case, a
logic "0" on this pin, when the COM20020-5
is accessed, enables data from the device to
the data bus to be read by the
microcontroller.
26
nWrite/
nWR/DIR Input. On a 68XX-like bus, this signal is
Direction
issued by the microcontroller as the
Read/nWrite signal to determine the
direction of data transfer. In this case, a
logic "1" selects a read operation, while a
logic "0" selects a write operation. In this
case, data is actually strobed by the nDS
signal. On an 80XX-like bus, this active low
signal is issued by the microcontroller to
indicate a write operation. In this case, a
logic "0" on this pin, when the COM20020-5
is accessed, enables data from the data bus
to be written to the device.
4