S1C63666 TECHNICAL MANUAL
EPSON
49
CHAPTER 4: PERIPHERAL CIRCUITS AND OPERATION (I/O Ports)
4.7.2 Mask option
The output specification of each I/O port during output mode can be selected from either complemen-
tary output or P-channel open drain output by mask option. This selection can be done in 1-bit units.
When P-channel open drain output is selected, do not apply a voltage exceeding the power supply
voltage to the port.
The mask option also permits selection of whether the pull-down resistor is used or not during input
mode. This selection can be done in 1-bit units.
When "without pull-down" during the input mode is selected, take care that the floating status does not
occur.
The pull-down resistor for input mode and output specification (complementary output or P-channel
open drain output) selected by mask option are effective even when I/O ports are used for input/output
of the serial interface.
4.7.3 I/O control registers and input/output mode
Input or output mode can be set for the I/O ports by writing data into the corresponding I/O control
registers IOCxx.
To set the input mode, write "0" to the I/O control register. When an I/O port is set to input mode, it
becomes high impedance status and works as an input port.
However, when the pull-down explained in the following section has been set by software, the input line
is pulled down only during this input mode.
To set the output mode, write "1" is to the I/O control register. When an I/O port is set to output mode, it
works as an output port, it outputs a high level (V
DD
) when the port output data is "1", and a low level
(V
SS
) when the port output data is "0".
If perform the read out in each mode; when output mode, the register value is read out, and when input
mode, the port value is read out.
At initial reset, the I/O control registers are set to "0", and the I/O ports enter the input mode.
The I/O control registers of the ports that are set as input/output for the serial interface can be used as
general purpose registers that do not affect the I/O control. (See Table 4.7.1.1.)
4.7.4 Pull-down during input mode
A pull-down resistor that operates during the input mode is built into each I/O port of the S1C63666.
Mask option can set the use or non-use of this pull-down.
The pull-down resistor becomes effective by writing "1" to the pull-down control register PULxx that
corresponds to each port, and the input line is pulled down during the input mode. When "0" has been
written, no pull-down is done.
At initial reset, the pull-down control registers are set to "1".
The pull-down control registers of the ports in which "gate direct" has been selected can be used as
general purpose registers.
Even when "with pull-down" has been selected, the pull-down control registers of the ports, that are set
as output for the serial interface, can be used as general purpose registers that do not affect the pull-down
control. (See Table 4.7.1.1.)
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.
