NEC mPD789026 Subseries, User Manual

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CHAPTER 4 PORT FUNCTIONS
User's Manual U11919EJ3V0UM00
77
4.2.5 Port 4
This is an 8-bit I/O port with output latch. Port 4 can be specified in the input or output mode in 1-bit units by
using port mode register 4 (PM4). When using P40 to P47 pins as input port pins, on-chip pull-up resistors can be
connected in 8-bit units by using the pull-up resistor option register (PUO).
The pins of this port are also used as the key return input.
RESET input sets port 4 to input mode.
Figure 4-8 shows the block diagram of port 4.
Caution When using port 4 for the key return function, it is necessary to set key return mode register 00.
For details of the settings, see Section 10.3 (5).
Figure 4-8. Block Diagram of P40 to P47
WR
KRM00
Internal Bus
V
DD0
P40/KR0 to
P47/KR7
WR
PUO
RD
WR
PORT
WR
PM
PUO4
Alternate
Function
Output Latch
(P40 to P47)
PM40 to PM47
KRM000 to KRM007
Selector
P-ch
KRM00 : Key return mode register 00
PUO : Pull-up resistor option register
PM : Port mode register
RD : Port 4 read signal
WR : Port 4 write signal