CHAPTER 4 PORT FUNCTIONS
4.2.1 Port 0
This is a 4-bit I/O port with an output latch. Port 0 can be specified in the input or output mode in 1-bit units by
using the port mode register 0 (PM0). When the P00 to P03 pins are used as input port pins, on-chip pull-up
resistors can be connected in 4-bit units by using pull-up resistor option register 0 (PU0).
Port 0 is set in the input mode when the RESET signal is input.
Figure 4-3 shows a block diagram of port 0.
Figure 4-3. Block Diagram of P00 to P03
VDD
WRPUO
PU00
P-ch
RD
WRKRM00
KRM000
WRPORT
Output latch
(P00 to P03)
P00/KR0 to
P03/KR3
W
RPM
PM00 to PM03
Alternate function
KRM00: Key return mode register 00
PU0:
PM:
RD:
Pull-up resistor option register 0
Port mode register
Port 0 read signal
WR:
Port 0 write signal
User’s Manual U15075EJ1V0UM00
81
NEC [ NEC ]
