RL78/F13, F14 CHAPTER 4 PORT FUNCTIONS
R01UH0368EJ0210 Rev.2.10 346
Dec 10, 2015
4.4 Port Function Operations
Port operations differ depending on whether the input or output mode is set, as shown below.
4.4.1 Writing to I/O port
(1) Output mode
A value is written to the output latch by a transfer instruction, and the output latch contents are output from the pin.
Once data is written to the output latch, it is retained until data is written to the output latch again.
The data of the output latch is cleared when a reset signal is generated.
(2) Input mode
A value is written to the output latch by a transfer instruction, but since the output buffer is off, the pin status does not
change. Accordingly, data can be written in byte units to a port having both input and output pins.
Once data is written to the output latch, it is retained until data is written to the output latch again.
The data of the output latch is cleared when a reset signal is generated.
4.4.2 Reading from I/O port
(1) Output mode
The output latch contents are read by a transfer instruction. The output latch contents do not change.
When the PMS0 bit in the port mode select register is set to 1, the pin level can be read from Pxx.
(2) Input mode
The pin status is read by a transfer instruction. The output latch contents do not change.
4.4.3 Operations on I/O port
(1) Output mode
An operation is performed on the output latch contents, and the result is written to the output latch. The output latch
contents are output from the pins.
Once data is written to the output latch, it is retained until data is written to the output latch again.
The data of the output latch is cleared when a reset signal is generated.
(2) Input mode
The pin level is read and an operation is performed on its contents. The result of the operation is written to the output
latch, but since the output buffer is off, the pin status does not change. Accordingly, data can be written in byte units
to a port having both input and output pins.
The data of the output latch is cleared when a reset signal is generated.
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