Epson S1C6S3N2 Technical Manual page 61

P00–P03, P10–P13:
I/O port data
(07DH, 0FDH)
S1C6S3N2 TECHNICAL HARDWARE
CHAPTER 4: PERIPHERAL CIRCUITS AND OPERATION (I/O Ports)
I/O port data can be read and output data can be set
through these ports.
• When writing data
When "1" is written :
When "0" is written :
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 ), and when "0" is written, the level goes low (V
DD
Port data can be written also in the input mode.
• When reading data out
When "1" is read out : High level
When "0" is read out : 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 output voltage level can be read. When the termi-
nal voltage is high (V
"1", and when the terminal voltage is low (V
"0".
Further, the built-in pull-down resistance goes ON during
read-out, so that the I/O port terminal is pulled down.
Note
- When the I/O port is set to the output mode and a low-impedance
load is connected to the port terminal, the data written to the
register may differ from the data read out.
- When the I/O port is set to the input mode and a low-level volt-
age (V ) is input, erroneous input results if the time constant of
SS
the capacitive load of the input line and the built-in pull-down
resistance load is greater than the read-out time. When the input
data is being read out, the time that the input line is pulled down
is equivalent to 1.5 cycles of the CPU system clock. However,
the electric potential of the terminals must be settled within 0.5
cycles. If this condition cannot be fulfilled, some measure must
be devised such as arranging pull-down resistance externally, or
performing multiple read-outs.
High level
Low level
) the port data that can be read is
DD
EPSON
).
SS
) the data is
SS
I-49