Port 0; Block Diagram Of P00 To P03 - NEC UPD789426 Series User Manual

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 setting 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.
WR
PUO
RD
WR
KRM00
WR
PORT
W
RPM
KRM00: Key return mode register 00
PU0: Pull-up resistor option register 0
PM: Port mode register
RD: Port 0 read signal
WR: Port 0 write signal
80
CHAPTER 4 PORT FUNCTIONS
Figure 4-3. Block Diagram of P00 to P03
PU00
KRM000
Output latch
(P00 to P03)
PM00 to PM03
Alternate function
User's Manual U15075EJ2V1UD
V
DD
P-ch
P00/KR0 to
P03/KR3