uPD789871 Subseries 8-Bit Single-Chip Microcontrollers PUM

4.2 Port Configuration
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A port consists of the following hardware.
CHAPTER 4 PORT FUNCTIONS
Table 4-2. Configuration of Port
Parameter Configuration
Control register Port mode register (PMm: m = 0 to 2)
Pull-up resistor option register 0 (PU0)
Pull-up option register B2 (PUB2)
Port Total: 33
CMOS I/O: 17
P-ch open-drain I/O: 8
P-ch open-drain output: 8
Pull-up resistor 17 (software control)
Pull-down resistor • Mask ROM versions: 16 (8 of these can be specified by the mask option)
• Flash memory versions: None
4.2.1 Port 0
This is a 8-bit I/O port with output latches. Port 0 can be specified as input or output mode in 1-bit units by using
port mode register 0 (PM0). When pins P00 to P07 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).
RESET input sets port 0 to input mode.
Figure 4-2 shows the block diagram of port 0.
Internal bus
WRPU0
RD
WRPORT
WRPM
PU0: Pull-up resistor option register 0
PM: Port mode register
RD: Port 0 read signal
WR: Port 0 write signal
Figure 4-2. Block Diagram of P00 to P07
PU00
Output latch
(P00 to P07)
PM00 to PM07
Selector
Preliminary User’s Manual U14938EJ1V0UM
VDD0
P-ch
P00 to P07