CHAPTER 4 PORT FUNCTIONS
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User’s Manual U11302EJ4V0UM
4.2 Port Configuration
A port consists of the following hardware.
Table 4-2. Port Configuration
Item
Configuration
Control registers
Port mode register (PMm: m = 0, 1, 2, 3, 7, 10, 11, 12)
Pull-up resistor option register (PUO)
Ports
Total: 74 (2 input, 16 output, 56 I/O)
Pull-up resistors
• Mask ROM versions
Total: 32 (software control: 27, mask option control: 5)
•
µ
PD78P0208 ... Total: 27
Pull-down resistors
• Mask ROM versions ... Total: 48 (mask option control: 48)
4.2.1 Port 0
Port 0 is a 5-bit I/O port with an output latch. The P01 to P03 pins can be set to input mode/output mode in 1-
bit units using port mode register 0 (PM0). The P00 and P04 pins are input-only port pins. When the P01 to P03
pins are used as input port pins, on-chip pull-up resistors can be connected to them in 3-bit units using the pull-
up resistor option register (PUO).
Alternate functions include external interrupt request input, external count clock input to the timer, and crystal
connection for subsystem clock oscillation.
RESET input sets port 0 to input mode.
Figures 4-2 and 4-3 show block diagrams of port 0.
Caution Because port 0 can also be used for external interrupt request input, when the port function
output mode is specified and the output level is changed, the interrupt request flag is set. Thus,
when the output mode is used, set the interrupt mask flag to 1.
