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M38C21F1DHP

SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER

MITSUBISHI ELECTRIC  

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MITSUBISHI MICROCOMPUTERS

38C2 Group

SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER

I/O PORTS

Direction Registers

The I/O ports P0–P6 have direction registers which determine the

input/output direction of each individual pin. Each bit in a direction

register corresponds to one pin, each pin can be set to be input port

or output port.

When “0” is written to the bit of the direction register, the correspond-

ing pin becomes an input pin. As for ports P0–P2, when “1” is written

to the bit of the direction register and the segment output disable

register, the corresponding pin becomes an output pin. As for ports

P3–P6, when “1” is written to the bit of the direction register, the

corresponding pin becomes an output pin.

If data is read from a pin set to output, the value of the port output

latch is read, not the value of the pin itself. Pins set to input are float-

ing. If a pin set to input is written to, only the port output latch is

written to and the pin remains floating.

Pull-up Control

Each individual bit of ports P0–P2 can be pulled up with a program

by setting direction registers and segment output disable registers 0

to 2 (addresses 0FF816 to 0FFA16).

The pin is pulled up by setting “0” to the direction register and “1” to

the segment output disable register.

By setting the PULL register (address 0FF116), ports P3–P6 can con-

trol pull-up with a program.

However, the contents of PULL register do not affect ports pro-

grammed as the output ports.

Segment output

disable register

“0”

Direction register

“1”

Initial state

“0”

Input port Input port

No pull-up Pull-up

“1”

Segment Port output

output

Fig. 10 Structure of ports P0 to P2

b7

b0

PULL register

(PULL : address 0FF116)

P30–P33 pull-up

P34–P37 pull-up

P40–P43 pull-up

P44–P47 pull-up

P50–P53 pull-up

P54–P57 pull-up

P60–P62 pull-up

Not used (return “0” when read)

0: No pull-up

1: Pull-up

b7

b0

Segment output disable register 0

(SEG0 : address 0FF816)

P00 pull-up

P01 pull-up

P02 pull-up

P03 pull-up

P04 pull-up

P05 pull-up

P06 pull-up

P07 pull-up

b7

b0

Segment output disable register 1

(SEG1 : address 0FF916)

P10 pull-up

P11 pull-up

P12 pull-up

P13 pull-up

P14 pull-up

P15 pull-up

P16 pull-up

P17 pull-up

b7

b0

Segment output disable register 2

(SEG2 : address 0FFA16)

P20 pull-up

P21 pull-up

P22 pull-up

P23 pull-up

P24 pull-up

P25 pull-up

P26 pull-up

P27 pull-up

0: No pull-up

1: Pull-up

Note: The PULL register and segment output disable register

affect only ports programmed as the input ports.

Fig. 11 Structure of PULL register and segment output disable register

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