Measurement of CMOS signals using PCI-DIO-96

[Endrek]

I am trying to measure a CMOS signal level with current limiter resistor (25k) on the output. But the CMOS device is not capable of sinking the input of the PCI-DIO-96 because of the 100k pull-up resistors on the board. Will the PCI-DIO96 work as an input if I remove the 100k resistor or use e.g. 500k instead?

[Filipe A.]

Hello;

When a digital board has a pull up resistor, that means the output line is a open collector type, so, a "external" connection needs to be made to the Vcc supply. Then, when a current is applied at the base of the transistor, the transistor switches and the ground (low state) is connected to the output lead. If no current is applied to the base of the transistor, then the Vcc level is being output at the output lead, meaning a high digital state.
The value of the resistor is chosen depending on the specifications of the transistor used as the gate. As my understanding, as long as you increase the values of that resistor you shouldn't have any problem as far as high current flowing trough the transistor when it switches. I've never tested that myself, but I
don't see why that couldn't be done.
But always keep in mind the warranty will void if you make such changes.
Hope this helps.
Filipe