I/O Ports - Fujitsu MB96300 series Hardware Manual

CHAPTER 13 I/O PORTS
13.1

I/O Ports

Each pin of the ports can be specified as input or output using the direction register, if
the corresponding peripheral does not use the pin. Before using a pin as input, it must
be enabled by setting the Port Input Enable register. When a pin is specified as input, the
logic level at the pin is read. When a pin is specified as output, the data register value is
read. The above also applies to a read operation for the read-modify-write instructions.
■ I/O ports
When a pin is used as an output of other peripheral function, the peripheral output value is read regardless of
the direction register value.
It is generally recommended that the read-modify-write instructions should not be used for setting the data
register prior to setting the port as an output. This is because the read-modify-write instruction in this case
results reading the logic level at the port rather than the register value.
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Figure 13.1-1 I/O port block diagram
Port Input Enable register read
Port Input Enable register
Port Input Enable register write
External Pin state read
Data register read
Data register
Data register write
Direction register
Direction register write
Direction register read
MB96300 Super Series Hardware Manual
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