Fujitsu 8FX Hardware Manual page 106

CHAPTER 6 I/O PORT
6.2 Configuration and Operations
■ Operations of I/O Port
●
Operation as an output port
• A pin becomes an output port if the bit in the DDRx register corresponding to that pin is set
to "1".
• For a pin shared with other peripheral functions, disable the output of such peripheral
functions.
• When a pin is used as an output port, it outputs the value of the PDRx register to external
pins.
• If data is written to the PDRx register, the value is stored in the output latch and is output to
the pin set as an output port as it is.
• Reading the PDRx register returns the PDRx register value.
●
Operation as an input port
• A pin becomes an input port if the bit in the DDRx register corresponding to that pin is set
to "0".
• For a pin shared with other peripheral functions, disable the output of such peripheral
functions.
• When using an analog input shared pin as an input port, set the corresponding bit in the A/D
input disable register (upper/lower) (AIDRH/AIDRL) to "1".
• If data is written to the PDRx register, the value is stored in the output latch but is not
output to the pin set as an input port.
• Reading the PDRx register returns the pin value. However, if the read-modify-write (RMW)
type of instruction is used to read the PDRx register, the PDRx register value is returned.
●
Operation as a peripheral function output pin
• A pin becomes a peripheral function output pin if the peripheral output function is enabled
by setting the output enable bit of a peripheral function corresponding to that pin.
• The pin value can be read from the PDRx register even if the peripheral function output is
enabled. Therefore, the output value of a peripheral function can be read by the read
operation on the PDRx register. However, if the read-modify-write (RMW) type of
instruction is used to read the PDRx register, the PDRx register value is returned.
●
Operation as a peripheral function input pin
• To set a pin as an input port, set the bit in the DDRx register bit corresponding to the input
pin of a peripheral function to "0".
• When using the analog input shared pin as another peripheral function input pin, configure
it as an input port, which is the same as the operation as an input port.
• Reading the PDRx register returns the pin value, regardless of whether the peripheral
function uses that pin as its input pin. However, if the read-modify-write (RMW) type of
instruction is used to read the PDRx register, the PDRx register value is returned.
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