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7480 Group and 7481 Group User's Manual

1-36

HARDWARE

1.10 Input/Output Pins

(2)

Switching of Programmable I/O Port Pins

Any pin of the programmable I/O ports P0, P1, P4, and P5 can be switched from input to output or

from output to input with the corresponding bit of their port direction registers.

• The pin is set to the input mode when the corresponding bit is ‘0’.

• The pin is set to the output mode when the corresponding bit is ‘1’.

Notes 1: In the 7480 Group, port P4 contains pins P40 and P41 only, while in the 7481 Group, port

P4 contains pins P40–P43. In addition, the 7480 Group does not have port P5, while the

7481 Group has port P5, consisting of P50–P53.

2: After system is released from reset, all of the programmable I/O port pins are set to the

input mode. (The corresponding direction registers are cleared to all ‘0’.)

3: When any of port pins P42, P43, and P50–P53 is used as an input port pin, clear the

corresponding bit of the port P4 and P5 direction registers to ‘0’. In addition, set the

corresponding input control bit of the port P4P5 input control register to ‘1’.

The 7480 Group does not have port pins P42, P43, and P50–P53; therefore, set the port

P4P5 input control register to ‘0016’.

(3)

Pull-up Control

When any pin of ports P0 and P1 is used as an input port pin, its pull-up can be controlled with the

corresponding bit of the port P0 and P1 pull-up control registers.

• A port pin is not pulled high when the corresponding bit is ‘0’.

• A port pin is pulled high when the corresponding bit is ‘1’.

Pull-up control is performed by the ON/OFF switch of a pull-up transistor. Pull-up control is valid only

when the pin is used for input and invalid when used for output or serial I/O.

Note: Port P0 controls the pull-up by the bit at one time. Port P1, however, controls the pull-up of

the high- or low-order four bits at one time. Even if only port P10 pin is pulled high, for

example, port pins P11–P13 are also pulled high simultaneously.

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