S1C63454 TECHNICAL MANUAL
EPSON
39
CHAPTER 4: PERIPHERAL CIRCUITS AND OPERATION (I/O Ports)
(1) Selection of port function
ESIF: Serial interface enable register (FF70H•D0)
Selects function for P10–P13.
When "1" is written: Serial interface input/output port
When "0" is written: I/O port
Reading: Valid
When using the serial interface, write "1" to this register and when P10–P13 are used as the I/O port,
write "0". The configuration of the terminals within P10–P13 that are used for the serial interface is
decided by the mode selected with the SCS1 and SCS0 registers (see Section 4.11).
In the slave mode, all the P10–P13 ports are set to the serial interface input/output port. In the master
mode, P10–P12 are set to the serial interface input/output port and P13 can be used as the I/O port.
At initial reset, this register is set to "0".
(2) I/O port control
P00–P03: P0 I/O port data register (FF42H)
P10–P13: P1 I/O port data register (FF46H)
I/O port data can be read and output data can be set through these registers.
• When writing data
When "1" is written: High level
When "0" is written: Low level
When an I/O port is set to the output mode, the written data is output unchanged from the I/O port
terminal. When "1" is written as the port data, the port terminal goes high (V
DD
), and when "0" is written,
the terminal goes low (V
SS
).
Port data can be written also in the input mode.
• When reading data
When "1" is read: High level
When "0" is read: Low level
The terminal voltage level of the I/O port is read out. When the I/O port is in the input mode the voltage
level being input to the port terminal can be read out; in the output mode the register value can be read.
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 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 input/output of the serial interface (P10–P12 or P10–
P13), 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 k
Ω
