CHAPTER 4: PERIPHERAL CIRCUITS AND OPERATION (I/O Ports)

When the terminal voltage is high (VDD) the port data that can be read is "1", and when the terminal voltage is low (VSS) the data is "0".

When "with pull-up resistor" has been selected with the mask option and the PUL register is set to "1", the built-in pull-up resister goes ON during input mode, so that the I/O port terminal is pulled up.

The data registers of the port, which are set for the special output (P22, P23) or input/output of the serial interface (P10–P13 or P30–P33), become general-purpose registers that do not affect the input/output.

Note: When in the input mode, I/O ports are changed from low to high by pull-up resistor, the rise of the waveform is delayed on account of the time constant of the pull-up resistor and input gate capaci- tance. Hence, when fetching input ports, set an appropriate wait time.

Particular care needs to be taken of the key scan during key matrix configuration.

Make this waiting time the amount of time or more calculated by the following expression.

10 ⋅ C ⋅ R

C:terminal capacitance 5 pF + parasitic capacitance ? pF

R:pull-up resistance 330 kΩ

IOC00–IOC03: P0 port I/O control register (FF40H)IOC10–IOC13: P1 port I/O control register (FF44H)IOC20–IOC23: P2 port I/O control register (FF48H)IOC30–IOC33: P3 port I/O control register (FF4CH)

The input and output modes of the I/O ports are set with these registers.

When "1" is written: Output mode

When "0" is written: Input mode

Reading: Valid

The input and output modes of the I/O ports are set in 1-bit unit.

Writing "1" to the I/O control register makes the corresponding I/O port enter the output mode, and writing "0" induces the input mode.

At initial reset, these registers are all set to "0", so the I/O ports are in the input mode.

The I/O control registers of the port, which are set for the special output (P22, P23) or input/output of the serial interface (P10–P13 or P30–P33), become general-purpose registers that do not affect the input/ output.

PUL00–PUL03: P0 port pull-up control register (FF41H)PUL10–PUL13: P1 port pull-up control register (FF45H)PUL20–PUL23: P2 port pull-up control register (FF49H)PUL30–PUL33: P3 port pull-up control register (FF4DH)

The pull-up during the input mode are set with these registers.

When "1" is written: Pull-up ON

When "0" is written: Pull-up OFF

Reading: Valid

The built-in pull-up resistor which is turned ON during input mode is set to enable in 1-bit units. (The pull-up resistor is included into the ports selected by the mask option.)

By writing "1" to the pull-up control register, the corresponding I/O ports are pulled up (during input mode), while writing "0" turns the pull-up function OFF.

At initial reset, these registers are all set to "1", so the pull-up function is set to ON.

The pull-up control registers of the ports in which the pull-up resistor is not included become the general purpose register. The registers of the ports that are set as special output or output for the serial interface can also be used as general purpose registers that do not affect the pull-up control.

The pull-up control registers of the port that are set as input for the serial interface function the same as the I/O port.

S1C63558 TECHNICAL MANUAL

EPSON

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