w78c31b Winbond Electronics Corp America, w78c31b Datasheet - Page 3

• Manufacturer Part Number: w78c31b
• Description: 8-bit Microcontroller
• Manufacturer: Winbond Electronics Corp America

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.
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:
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 W78C31B 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.
P3.0
P3.1
P3.2
P3.3
P3.4
P3.5
P3.6
P3.7
PIN
RXD Serial Receive Data
TXD Serial Transmit Data
INT0 External Interrupt 0
T0 Timer 0 Input
T1 Timer 1 Input
RD Data Read Strobe
INT1 External Interrupt 1
WR Data Write Strobe
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ALTERNATE FUNCTION
Publication Release Date: October 1997
W78C31B
Revision A3