How to set the initial value on a DIO output port line?

[KevinKiller]

I'm using a PCI-DIO-24 a.k.a. PCI-6503

I'm talking about setting the initial value
before switching to Output mode.

I know the card powers up in input mode, and I first have to set the mode to Output before I can change the DIO lines. I need to be able to setup the card such that +5V appears on the DIO lines immediatly after I set the port to Output mode. Right now, when I set the mode to Output, 0V appears on the DIO lines, then I write ones to the output port and +5V appears. This causes a small pulse which is messing up my equipment.

How can I set up the PCI-6503 such that when I set the port mode to Output, +5V appears on the DIO lines?

K.

[Sonya W.]

Whenever a PCI-650x board is configured for output, its digital lines will always reset to logic low. The glitch that is seen is around a 5 ms dip low from the time of the configuration until the software gives an output signal.

The workaround is to set the jumper on your board which configures the power-up (input) state of the lines. You can set the power-up state of the lines to low, and then there will not be a dip after configuration. If this power-up state is not satisfactory, then an inverter can be used on the output to switch the logic of the lines.

The Developer Zone article linked below contains additional information on this topic, including information on the 653x boards which do not reset to logic low when configured for output.

What Is the State of My Board's DIO Lines When My Computer First Turns On?

Sonya Wornson
Applications Engineer
National Instruments