NEC switch - Manual (Page 60)

CHAPTER 4 PORT FUNCTIONS
User’s Manual U12978EJ3V0UD
60
4.2.1 Port 0
This is an 8-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 port mode register 0 (PM0). When the P00 to P07 pins are used as input port pins, on-chip pull-up resistors
can be connected in 8-bit units by using pull-up resistor option register 0 (PU0). CMOS output or N-ch open-drain
output can also be specified in 8-bit unit by using port output mode register 0 (POM0).
Port 0 is set in the input mode when the RESET signal is input.
Figure 4-2 shows a block diagram of port 0.
Figure 4-2. Block Diagram of P00 to P07
RD
V DD0
P00 to P07
WR
PU0
WR PORT
WR PM
Output latch
(P00 to P07)
PM00 to PM07
PU00
P-ch
P-ch
N-ch
V DD0
POM00
Internal bus
Selector
WR POM0
POM0: Port output mode register 0
PU0: Pull-up resistor option register 0
PM: Port mode register
RD: Port 0 read signal
WR: Port 0 write signal