I-50
EPSON
S1C6S3N2 TECHNICAL HARDWARE
CHAPTER 4: PERIPHERAL CIRCUITS AND OPERATION (I/O Ports)
The input and output modes of the I/O ports can be set
with these registers.
When "1" is written :
Output mode
When "0" is written :
Input mode
Read-out :
Valid
The input and output modes of the I/O ports are set in units
of four bits. IOC0 sets the mode for P00–P03, and IOC1 sets
the mode for P10–P13.
Writing "1" to the I/O control register makes the correspond-
ing I/O port enter the output mode, and writing "0" induces
the input mode.
At initial reset, these two registers are set to "0", so the I/O
ports are in the input mode.
(1) When the I/O port is being read out, the built-in pull-
down resistance of the I/O port goes ON. Consequently,
if data is read out while the CPU is running in the OSC3
oscillation circuit, data must be read out continuously for
about 500 µs.
(2) When the I/O port is set to the output mode and the data
register has been read, the terminal data instead of the
register data can be read out. Because of this, if a low-
impedance load is connected and read-out performed, the
value of the register and the read-out result may differ.
Programming notes
IOC0, IOC1:
I/O control registers
(07EH·D0, 0FEH·D0)
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