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EPSON
S1C63666 TECHNICAL MANUAL
CHAPTER 4: PERIPHERAL CIRCUITS AND OPERATION (I/O Ports)
IOC00–IOC03: P0 port I/O control register (FF40H)
IOC10–IOC13: P1 port I/O control register (FF44H)
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 input/output of the serial interface (P10–P13),
become general-purpose registers that do not affect the input/output.
PUL00–PUL03: P0 port pull-down control register (FF41H)
PUL10–PUL13: P1 port pull-down control register (FF45H)
The pull-down during the input mode are set with these registers.
When "1" is written: Pull-down On
When "0" is written: Pull-down Off
Reading: Valid
The built-in pull-down resistor which is turned on during input mode is set to enable in 1-bit units. (The
pull-down resistor is included into the ports selected by mask option.)
By writing "1" to the pull-down control register, the corresponding I/O ports are pulled down (during
input mode), while writing "0" disables the pull-down function.
At initial reset, these registers are all set to "1", so the pull-down function is enabled.
The pull-down control registers of the ports in which the pull-down resistor is not included become the
general purpose register. The registers of the ports that are set as output for the serial interface can also be
used as general purpose registers that do not affect the pull-down control.
The pull-down control registers of the port that are set as input for the serial interface function the same
as the I/O port.
4.7.6 Programming note
When in the input mode, I/O ports are changed from high to low by pull-down resistor, the fall of the
waveform is delayed on account of the time constant of the pull-down 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-down resistance 375 k
Ω
(Max.)
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