I/O Ports - Fujitsu MB90390 Series Hardware Manual

CHAPTER 10 I/O PORTS
10.1

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. 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 (RMW)
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 (RMW) 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 (RMW)
instruction in this case results reading the logic level at the port rather than the register value.
Figure 10.1-1 is a block diagram of the I/O ports.
Internal data bus
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Figure 10.1-1 I/O Port Block Diagram
Data register read
Data register
Data register write
Direction register
Direction register write
Direction register read
Pin