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5.5 PORT 4
Port 4 is an 8-bit I/O port with an output latch. The memory expansion mode register (MM) can put all 8 bits of
this port in either the input or output mode at one time. Each pin has a software-programmable built-in pull-up
resistor, and can drive an LED directly.
When an external memory or I/O device is expanded, port 4 functions as a time-division address/data bus (AD0
through AD7).
For the µ PD78213, port 4 functions only as a time-division address/data bus (AD0 through AD7).
When the RESET signal is input, port 4 becomes an input port (high output impedance), and the contents of the
output latch become undefined.
Fig. 5-20 Connection of Pull-Up Resistors (Port 3)
(PUO)
PUO3
Chapter 5 Port Functions
V
DD
• • •
Port 3 mode
register (PM3)
P30
P31
P32
P36
P37
75
5
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