NEC uPD78P078 - Manual (Page 136)

136
CHAPTER 6 PORT FUNCTIONS
6.2 Port Configuration
A port consists of the following hardware:
Table 6-3. Port Configuration
Item Configuration
Control register Port mode register (PMm: m = 0 to 3, 5 to 10, 12, 13)
Pull-up resistor option register (PUOH, PUOL)
Memory expansion mode register (MM) Note
Key return mode register (KRM)
Port Total: 88 ports (2 inputs, 86 inputs/outputs)
Pull-up resistor • Mask ROM versions..... Total: 86 pins
(software-specifiable for 78 pins and mask option for 8 pins)
•
µ
PD78P078 (or 78P078Y) ..... Total: 78 pins
Note MM specifies port 4 input/output.
6.2.1 Port 0
Port 0 is an 8-bit input/output port with output latch. P01 to P06 pins can specify the input mode/output mode in
1-bit units with the port mode register 0 (PM0). P00 and P07 pins are input-only ports. When P01 to P06 pins are
used as input ports, an on-chip pull-up resistor can be used in 6-bit units with a pull-up resistor option register L (PUOL).
Dual-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 6-2 and 6-3 show block diagrams of port 0.
Caution Because port 0 also serves 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.