SIC63616-(Rev. 1.0) NO. P57
3240-0412
• When reading data
When "1" is read:
High level
When "0" is read:
Low level
When the I/O port is placed into input mode, the voltage level being input to the port terminal can be read
out. When the terminal voltage is high (V
DD
), the port data that can be read is "1", and when the terminal
voltage is low (V
SS
) the read data is "0".
When the pull-down resistor option has been selected and the PULxx register is set to "1", the built-in pull-
down resistor goes on during input mode, so that the I/O port terminal is pulled down.
When the I/O port is placed into output mode, the register value is read. Therefore, when using the data
register of a port that is not used for signal input/output as a general-purpose register, set the port to out-
put mode.
At initial reset, these registers are set to "1".
The data register of the port, which is set for an input/output of the serial interface or R/f converter or a
special output, becomes a general-purpose register that does not affect the input/output status.
Note: When I/O ports set in input mode is changed from high to low by the pull-down resistor, the fall of
the waveform is delayed on account of the time constant of the pull-down resistor and input gate
capacitance. Hence, when fetching input data, 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.)
IOC00–IOC03: P0 port I/O control register (FF21H)
IOC10–IOC13: P1 port I/O control register (FF25H)
IOC20–IOC23: P2 port I/O control register (FF29H)
IOC40–IOC43: P4 port I/O control register (FF31H)
Sets the I/O ports to input or output mode.
When "1" is written: Output mode
When "0" is written: Input mode
Reading: Valid
The input/output mode of the I/O ports are set in 1-bit units.
Writing "1" to the I/O control register places the corresponding I/O port into output mode, and writing "0"
sets input mode.
At initial reset, these registers are all set to "0", so the I/O ports are placed in input mode.
The I/O control register of the port, which is set for an input/output of the serial interface or R/f converter
or a special output, becomes a general-purpose register that does not affect the input/output status.
PUL00–PUL03: P0 port pull-down control register (FF22H)
PUL10–PUL13: P1 port pull-down control register (FF26H)
PUL20–PUL23: P2 port pull-down control register (FF2AH)
PUL40–PUL43: P4 port pull-down control register (FF32H)
Enables the pull-down during input mode.
When "1" is written: Pull-down On
When "0" is written: Pull-down Off
Reading: Valid