
107
μPD780948, μPD78F0948, μPD780949, μPD78F0949
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 input/output 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.
(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.
Caution:
In the case of 1-bit memory manipulation instruction, although a single bit is manipulated
the port is accessed as an 8-bit unit. Therefore, on a port with a mixture of input and
output pins, the output latch contents for pins specified as input are undefined except
for the manipulated bit.
5.4.2 Reading from input/output port
(1) Output mode
The output latch contents are read by a transfer instruction. The output latch contents do not change.
(2) Input mode
T he pin status is read by a transfer instruction. The output latch contents do not change.
5.4.3 Operations on input/output 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.
(2) Input mode
The output latch contents are undefined, but since the output buffer is OFF, the pin status does not
change.
Caution:
In the case of 1-bit memory manipulation instruction, although a single bit is manipulated
the port is accessed as an 8-bit unit. Therefore, on a port with a mixture of input and
output pins, the output latch contents for pins specified as input are undefined, even
for bits other than the manipulated bit.