Programming Note - Epson S1C6P366 Technical Manual

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)
IOC40–IOC43: P4 port I/O control register (FF50H)
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 ports that are set as input/output for the serial interface or A/D con-
verter can be used as 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 isavailable for the P10–P13, P20–P23, P30–P33 ports.)
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 registers of the ports that are set as input/output for the serial interface or A/D converter can 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.

4.6.6 Programming 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 capacitance.
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 300 kΩ
S1C6P366 TECHNICAL MANUAL
CHAPTER 4: PERIPHERAL CIRCUITS AND OPERATION (I/O Ports)
EPSON
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