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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.

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