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MSM80C48/49/50, MSM80C35/39/40

PIN DESCRIPTIONS

Symbol

Type

Description

(PORT 1)

8-bit quasi-bidirectional port

I/O

(PORT 2)

8-bit quasi-bidirectional port

The high-order four bits of external program memory addresses can be output

from P2.0-P2.3, to which the I/O expander MSM82C43RS may also be connected.

I/O

(BUS)

Bidirectional port

The low-order eight bits of external program memory address can be output

from this port, and the addressed instruction is fetched under the control of

PSEN signal. Also, the external data memory address is output, and data is

read and written synchronously using RD and WR signals.

The port can also serve as either a statically latched output port or a

non-latching input port.

I/O

T0

(Test 0)

The input can be tested with the conditional jump instructions JT0 and JNT0.

The execution of the ENT0 CLK instruction causes a clock output.

I/O

T1

(Test 1)

The input can be tested with the conditional jump instructions JT1 and JNT1.

The execution of a STRT CNT instruction causes an internal counter input.

I

INT

(Interrupt)

Interrupt input. If interrupt is enabled, INT input initiates an interrupt.

Interrupt is disabled after a reset.

Also testable with a JNI instruction. Can be used to terminate the power-down

mode. (Active "0" level)

I

RD

(Read)

A signal to read data from external data memory. (Active "0" level)

O

WR

(Write)

A signal to write data to external data memory. (Active "0" level)

O

ALE

Address &

Data Latch

Clock

This signal is generated in each cycle. It may be used as a clock output.

External data memory or external program memory is addressed upon the

falling edge. For the external ROM, this signal is used to latch the bus port data

upon the ALE signal rise-up after the execution of the OUTL BUS, A instruction.

O

PSEN Program

Store Enable

A signal to fetch an instruction from external program memory

(Active "0" level)

O

RESET

RESET input initialize the processor. (Active "0" level)

Used to terminate the power-down mode.

I

SS

(Single Step)

A program is executed step by step. This pin can also be used to control

internal oscillation when the power-down mode is reset.

(Active "0" level)

I

EA

(External Access)

When held at high level, all instructions are fetched from external memory.

(Active "1" level)

I

PROG

(Expander Strobe)

This output strobes the MSM82C43RS I/O expander.

O