Specifications

18 PCI-1757UP User's Manual
• Output status can be read back.
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 sets via
the switch. Table 3-1 shows the format of a control word.
Bit Description
D0 Port C lower bits 0: output; 1: input
D1 Port B 0: output; 1: input
D2 Don't care
D3 Port C higher bits 0: output; 1: input
D4 Port A 0: output; 1: input
D5 Don't care
D6 Don't care
D7 HW/SW 0: SW; 1: HW
Table 3-1: Bit map of port configuration register
Note: A control word has no effect if the corresponding 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.