W78C32C
PIN DESCRIPTION
P0.0−P0.7
Port 0, Bits 0 through 7. Port 0 is a bidirectional I/O port. This port also provides a multiplexed low
order address/data bus during accesses to external memory.
P1.0−P1.7
Port 1, Bits 0 through 7. Port 1 is a bidirectional I/O port with internal pull-ups. Pins P1.0 and P1.1
also serve as T2 (Timer 2 external input) and T2EX (Timer 2 capture/reload trigger), respectively.
P2.0−P2.7
Port 2, Bits 0 through 7. Port 2 is a bidirectional I/O port with internal pull-ups. This port also provides
the upper address bits for accesses to external memory.
P3.0−P3.7
Port 3, Bits 0 through 7. Port 3 is a bidirectional I/O port with internal pull-ups. All bits have alternate
functions, which are described below:
PIN
P3.0
P3.1
P3.2
P3.3
P3.4
P3.5
P3.6
P3.7
ALTERNATE FUNCTION
RXD Serial Receive Data
TXD Serial Transmit Data
INT0 External Interrupt 0
INT1 External Interrupt 1
T0 Timer 0 Input
T1 Timer 1 Input
WR Data Write Strobe
RD Data Read Strobe
EA
External Address Input, active low. This pin forces the processor to execute out of external ROM.
This pin should be kept low for all W78C32C operations.
RST
Reset Input, active high. This pin resets the processor. It must be kept high for at least two machine
cycles in order to be recognized by the processor.
ALE
Address Latch Enable Output, active high. ALE is used to enable the address latch that separates the
address from the data on Port 0. ALE runs at 1/6th of the oscillator frequency. A single ALE pulse is
skipped during external data memory accesses. ALE goes to a high state during reset with a weak
pull-up.
-3-
Publication Release Date: July 1999
Revision A2
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