FUJITSU F2MCTM-16LX - Manual (Page 187)

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CHAPTER 10 I/O PORTS
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Reading the port data register
The value obtained when reading the port data register (PDR) depends on the status of the port direction
register (DDR) and status of the peripheral function connected to the pin.
The following shows the value obtained by each combination.
Value of DDR Output state of peripheral
function
Reading value
0 (input) Enabled Output value from peripheral
function
1 (output) Enabled Output value from peripheral
function
0 (input) Disabled Pin state
1 (output) Disabled Value of output latch
Further, when using as input by peripheral function, set the DDR of the connected pin to "0" (input).