CHAPTER 4 PORT FUNCTIONS
4.2.8 Port 8 (µPD789426, 789436 Subseries only)
This is a 2-bit I/O port with an output latch. Port 8 can be specified in the input or output mode in 1-bit units by
using port mode register 8 (PM8). When using pins P80 and P81 as input port pins, on-chip pull-up resistors can be
connected in 1-bit units by using pull-up resistor option register B8 (PUB8).
This port is set in the input mode when the RESET signal is input.
Figure 4-16 shows a block diagram of port 8.
Figure 4-16. Block Diagram of P80 and P81
V
DD
WRPUB8
PUB80, PUB81
P-ch
RD
WRPORT
Output latch
(P80, P81)
P80, P81
WRPM
PM80, PM81
PUB8: Pull-up resistor option register B8
PM: Port mode register
RD: Port 8 read signal
WR: Port 8 write signal
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User’s Manual U15075EJ1V0UM00
NEC [ NEC ]
