Renesas rl78 User Manual
RL78/G1A
CHAPTER 4 PORT FUNCTIONS
R01UH0305EJ0200 Rev.2.00
115
Jul 04, 2013
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. Therefore, byte data can be written to the ports used for both input and output.
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.
(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. 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.