4 port 4 – NEC switch User Manual

Page 68

CHAPTER 4 PORT FUNCTIONS

User’s Manual U12978EJ3V0UD

4.2.4 Port 4

This is an 8-bit I/O port with an output latch. Port 4 can be specified in the input or output mode in 1-bit units by

using port mode register 4 (PM4). When using P40 to P47 pins as input port pins, on-chip pull-up resistors can be

connected in 8-bit units by using pull-up resistor option register 0 (PU0).

The port is also used as a key return input.

This port is set in the input mode when the RESET signal is input.

Figure 4-10 shows a block diagram of port 4.

Caution

When using the pins of port 4 as the key return, key return mode register 00 (KRM00) must be

set according to the function to be used. For how to set the register, see Section 11.3 (5) Key

return mode register 00 (KRM00).

Figure 4-10. Block Diagram of P40 to P47

KRM

Internal bus

DD0

P40/KR00 to
P47/KR07

PU0

PORT

PU04

Alternate

function

Output latch

(P40 to P47)

PM40 to PM47

KRM000 to

KRM007

Selector

P-ch

KRM00:

Key return mode register 00

PU0:

Pull-up resistor option register 0

PM:

Port mode register

RD:

Port 4 read signal

WR:

Port 4 write signal