Advantech PCI-1757UP, User Manual

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17 Chapter 3
3.2.3 Input/Output Control
A control word can be written to a port's configuration register (Base+3)
to set the port as an input or an output port, unless the ports are set via the
switch. Table 3-1 shows the format of a control word.
Table 3.1: Bit Map of Port Configuration Register
Bit Description
D0 Port C lower bits 0: output; 1: input
D1 Port B 0: output; 1: input
D2 Ignore
D3 Port C higher bits 0: output; 1: input
D4 Port A 0: output; 1: input
D5 Ignore
D6 Ignore
D7 HW/SW 0: SW; 1: HW
Note: A control word has no effect if the correspond-
ing port is set as an output port by the SMD
switch SW2. D7 is a read only bit for identifying
the SMD switch SW2 position 1 is ON or OFF.
D7 = 0 means the I/O configuration is set by
configuration register (SW); D7 = 1 means the I/
O configuration is set by SMD switch SW2
(HW). When D7= 1, read the value of D4, D3,
D1 and D0 mapping the SW2 location 3,4,5 and
6, respectively.
Warning! Before setting any port as an output port via
software, make sure that a safe output value
has also been set. An output voltage will
appear at the pins immediately following the
control word taking effect. If no output value
was specified, the value will be indeterminate
(either 0 or 1), which may cause a dangerous
condition.