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Chapter 5 Port Functions
5
Fig. 5-20 Connection of Pull-Up Resistors (Port 3)
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.
Internal bus
VDD
P30
P31
P32
P36
P37
Input buffer
PUO3
(PUO)
•••
•••
•••
•••
Port 3 mode
register (PM3)