Port 12 - NEC 78K0S/KB1+ User Manual

WR
PU
RD
WR
PORT
Output latch
WR
PM
PU4: Pull-up resistor option register 4
P4: Port register 4
PM4: Port mode register 4
RD: Read signal
WR××: Write signal
4.2.5

Port 12

Port 12 is a 4-bit I/O port with an output latch. Each bit of this port can be set to the input or output mode by using
port mode register 12 (PM12). When the P120 and P123 pins are used as an input port, an on-chip pull-up resistor
can be connected by using pull-up resistor option register 12 (PU12).
The P121 and P122 pins are also used as the X1 and X2 pins of the system clock oscillator. The functions of the
P121 and P122 pins differ, therefore, depending on the selected system clock oscillator. The following three system
clock oscillators can be used.
(1) High-speed internal oscillator
The P121 and P122 pins can be used as I/O port pins.
(2) Crystal/ceramic oscillator
The P121 and P122 pins cannot be used as I/O port pins because they are used as the X1 and X2 pins.
60
CHAPTER 4 PORT FUNCTIONS
Figure 4-11. Block Diagram of P43
PU4
PU43
Alternate
function
P4
(P43)
PM4
PM43
Alternate
function
User's Manual U17446EJ3V1UD
V
DD
P-ch
P43/TxD6/INTP1