Port 4 - NEC 78K0S/KU1+ User Manual

RD: Read signal
Caution Because the P34 pin functions alternately as the RESET pin, if it is used as an input port pin, the
function to input an external reset signal to the RESET pin cannot be used. The function of the
port is selected by the option byte. For details, refer to CHAPTER 15 OPTION BYTE.
Also, since the option byte is referenced after the reset release, if low level is input to the RESET
pin before the referencing, then the reset state is not released. When it is used as an input port
pin, connect the pull-up resistor.
4.2.3

Port 4

Port 4 is a 2-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 4 (PM4)
be connected in 1-bit units by using pull-up resistor option register 4 (PU4).
Reset signal generation sets port 4 to the input mode.
Figures 4-7 shows the block diagram of port 4.
Note At program initialization, set PM41, PM42, and PM44 to PM47 to "0".
CHAPTER 4 PORT FUNCTIONS
Figure 4-6. Block Diagram of P34
RD
Reset
Option
byte
Note
. When the P40 and P43 pins are used as an input port, an on-chip pull-up resistor can
User's Manual U18172EJ2V0UD
P34/RESET
57