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2 port 1 – NEC switch User Manual

Page 61

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CHAPTER 4 PORT FUNCTIONS

User’s Manual U12978EJ3V0UD

61

4.2.2 Port 1

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

using port mode register 1 (PM1). When the P10 to P17 pins are used 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). CMOS output or N-ch open-drain

output can also be specified in 8-bit unit by using port output mode register 0 (POM0).

Port 0 is set in the input mode when the RESET signal is input.

Figure 4-3 shows a block diagram of port 1.

Figure 4-3. Block Diagram of P10 to P17

POM0:

Port output mode register 0

PU0:

Pull-up resistor option register 0

PM:

Port mode register

RD:

Port 1 read signal

WR:

Port 1 write signal

RD

V

DD0

P10 to P17

WR

POM0

WR

PU0

WR

PORT

WR

PM

Output latch

(P10 to P17)

PM10 to PM17

PU01

P-ch

P-ch

N-ch

V

DD0

POM01

Internal bus

Selector