Port 4 - NEC 78K0S/KA1+ 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 17 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 6-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). When the P40 to P45 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 4 (PU4).
Alternate functions include external interrupt request input, serial interface data I/O, and timer output.
Reset signal generation sets port 4 to the input mode.
Figures 4-6 to 4-9 show the block diagrams of port 4.
CHAPTER 4 PORT FUNCTIONS
Figure 4-5. Block Diagram of P34
RD
Reset
Option
byte
User's Manual U16898EJ3V0UD
P34/RESET
53