Port 4 - NEC mPD780344 Series User Manual

8-bit single-chip microcontrollers

Table of Contents

4.2.5 Port 4

Port 4 is a 4-bit I/O port with an output latch. The P40 to P43 pins can be set to input mode/output mode in 1-

bit units using port mode register 4 (PM4).

At the falling edge of any of the P40 to P43 pins, the interrupt request flag (KRIF) can be set to 1.

RESET input sets port 4 to input mode.

Figure 4-11 shows a block diagram of port 4 and Figure 4-12 shows a block diagram of the falling edge detector,

respectively.

Cautions 1. When using the falling edge detection interrupt (INTKR), be sure to set the memory expansion

mode register (MEM) to 01H.

2. The falling edge can be detected only when a falling edge occurs while all the P40 to P43 pins

The falling edge of another pin cannot be detected while even one of the P40 to P43 pins is

PU: Pull-up resistor option register

PM: Port mode register

RD: Port 4 read signal

WR: Port 4 write signal

CHAPTER 4 PORT FUNCTIONS

Figure 4-11. Block Diagram of P40 to P43

PU40 to PU43

Output latch

(P40 to P43)

PM40 to PM43

Figure 4-12. Block Diagram of Falling Edge Detector

"1" when MEM = 01H

User's Manual U15798EJ2V0UD

Falling edge