RL78/G1H CHAPTER 5 PORT FUNCTIONS
R01UH0575EJ0120 Rev. 1.20 Page 85 of 920
Dec 22, 2016
5.4 Port Function Operations
Port operations differ depending on whether the input or output mode is set, as shown below.
5.4.1 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.
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.
5.4.2 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.
(2) Input mode
The pin status is read by a transfer instruction. The output latch contents do not change.
5.4.3 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. Therefore, byte data can
be written to the ports used for both input and output.
The data of the output latch is cleared when a reset signal is generated.
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