DIO high voltage setting

[sarahc]

Is DIO high voltage always 5V?! Could I change it and how? Because my device input voltage high is not 5V.
One more question, I measure 5V when the line state of Write to Digital Line is False. What's wrong?

Thanks~

[dhuff]

Some of the NI cards allow you to change the digital IO high & low voltages, but most cards will not, it depends on your hardware. Many of the DIO cards are 0-5V digital logic, which means that anything above about 2.4V is a digital High, and anything below about 0.8V is a digtal low. You can use external analog circuits to change different voltages into 5V logic levels. We would need more details about your hardware to know.
As for the second question, many digital circuits are designed to be used with a load, so if you do not hook a load onto the output, it will float high, regardless of what state the logic is.
Try connecting a 10K ohm resistor from the output to 5V, just to simulate a load, then measure the voltage out of those digital pins. If that doesn't
work, try connecting the 10K ohm resistor from ground to the output, one of those ideas will work, depending on which type of digital lines you have.

[sarahc]

My card is PCI-6025E.
I use DIO0 and DIO1 only and initial DIO0 and DIO1 is 5V. others DIO2~DIO7 is 0V. PA,PB,PC is 5V.
And I connect 10kohm from DIO0 to 5V, Then I measure the digital pins which voltage is still 5V. Connect 10kohm to GND, the voltage is still 5V. Nothing change.

[dhuff]

your card is only capable of 0-5V signals, so if you want other voltage levels you will need an external converter.
Before we go too much fatrher, do you have the DIO pins or ports configured in MAX? (That is the NI Measurement & Automation Explorer) MAX will setup the channel names and directions for you, and once you have a channel defined, click on the Test button, just to see if it is configured.