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7480 Group and 7481 Group User's Manual

1-35

HARDWARE

1.10 Input/Output Pins

1.10.3 I/O Ports

(1)

Writes to and Reads from I/O Port Pins

Pin used for input (Ports P0 to P5)

• A read: When reading from port register corresponding to each port, the input value (state of the

pin) is read; the contents of port latch is not read.

• A write: When writing to port register corresponding to each port, data is written only into the port

latch; the state of the pin is unaffected.

Pin used for output (Ports P0, P1, P4, and P5)

• A read: When reading from port register corresponding to each port, the written value into the port

latch is read; the state of the pin is not read. Therefore, even if the output voltage is

affected by the external load etc., the last output value can correctly be read.

• A write: When writing to port register corresponding to each port, data written into a bit of the port

Figure 1.10.10 shows a write and a read of an I/O port pin.

Figure 1.10.10 Write and Read of I/O Port Pin

Note: The P-channel transistor and the N-channel transistor are in a cut-off state.

Pins used for input

• By reading from port register, input level of pin

can be read.

• By writing to port register, writing to port latch is

performed.

Port register

(When Writing)

Port direction

(‘0’)

‘H’ level output

‘L’ level output

(Note)

Port register

(When Reading)

Port register

(When Writing)

Port register

(When Reading)

Port direction

(‘1’)

Pins used for output

• By reading from port register, port latch can be read.

• By writing to port register, output value can be set.

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