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CHAPTER 6 PORT FUNCTIONS
6.2.10 Port 8
Port 8 is an 8-bit input/output port with output latch. P80 to P87 pins can specify the input mode/output mode in
1-bit units with the port mode register 8 (PM8). When pins P80 to P87 are used as input ports, an on-chip pull-up
resistor can be connected to them in 8-bit units with a pull-up resistor option register H (PUOH).
Dual-functions include the address bus function in external memory expansion mode.
RESET input sets port 8 to input mode.
Figure 6-17 shows block diagram of port 8.
Figure 6-17. Block Diagram of P80 to P87
PUO : Pull-up resistor option register
PM : Port mode register
RD : Port 8 read signal
WR : Port 8 write signal
P-ch
WR
PM
WR
PORT
RD
WR
PUO
V
DD
Selector
PUO8
Output Latch
(P80 to P87)
PM80 to PM87
Internal bus
P80/A0 to
P87/A7