¡ Semiconductor
MSM82C55A-2RS/GS/VJS
PIN DESCRIPTION
Pin No.
Item
Input/Output
Function
These are three-state 8-bit bidirectional buses used to write and
read data upon receipt of the WR and RD signals from CPU and also
used when control words and bit set/reset data are transferred from
CPU to MSM82C55A-2.
Bidirectional
Data Bus
Input and
Output
D7 - D0
This signal is used to reset the control register and all internal
registers when it is in high level. At this time, ports are all made into
the input mode (high impedance status).
all port latches are cleared to 0.
and all ports groups are set to mode 0.
RESET
Input
Input
Reset Input
When the CS is in low level, data transmission is enabled with CPU.
When it is in high level, the data bus is made into the high impedance
status where no write nor read operation is performed. Internal
registers hold their previous status, however.
Chip Select
Input
CS
When RD is in low level, data is transferred from MSM82C55A-2 to
CPU.
RD
Read Input
Write Input
Input
Input
When WR is in low level, data or control words are transferred from
CPU to MSM82C55A-2.
WR
By combination of A0 and A1, either one is selected from among
port A, port B, port C, and control register. These pins are usually
connected to low order 2 bits of the address bus.
Port Select Input
(Address)
A0, A1
Input
These are universal 8-bit I/O ports. The direction of inputs/ outputs
can be determined by writing a control word. Especially, port A can
be used as a bidirectional port when it is set to mode 2.
Input and
Output
PA7 - PA0
PB7 - PB0
Port A
Port B
These are universal 8-bit I/O ports. The direction of inputs/outputs
ports can be determined by writing a control word.
Input and
Output
These are universal 8-bit I/O ports. The direction of inputs/outputs
can be determined by writing a control word as 2 ports with 4 bits
each. When port A or port B is used in mode 1 or mode 2 (port A
only), they become control pins. Especially, when port C is used as
an output port, each bit can set/reset independently.
Input and
Output
PC7 - PC0
Port C
VCC
–
–
–
–
+5V power supply.
GND
GND
9/26
OKI [ OKI ELECTRONIC COMPONETS ]
