Port 3 - NEC 78K0S/KB1+ User Manual

4.2.3

Port 3

Pins P30 to P33 constitute 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 3 (PM3). When the P30 to P33 pins are used as an input port, an on-chip
pull-up resistor can be connected in 1-bit units by using pull-up resistor option register 3 (PU3).
The P30 and P31 pins are also used for both timer I/O and external interrupt request input pin functions.
Generation of reset signal sets port 3 to the input mode.
P34 is a 1-bit input-only port. This pin is also used as a RESET pin, and when the power is turned on, this is the
reset function.
For settings of alternate function, refer to CHAPTER 18 OPTION BYTE. When using P34 as input port, pull up the
P34 pin by using external resistor.
Figures 4-4 to 4-7 show the block diagrams of port 3.
WR
PU
RD
WR
PORT
WR
PM
PU3: Pull-up resistor option register 3
P3: Port register 3
PM3: Port mode register 3
RD: Read signal
WR××: Write signal
54
CHAPTER 4 PORT FUNCTIONS
Figure 4-4. Block Diagram of P30
PU3
PU30
Alternate
function
P3
Output latch
(P30)
PM3
PM30
User's Manual U17446EJ3V1UD
V
DD
P-ch
P30/TI000/INTP0