The driver support for a counter/timer board such as the NI PCI-6624 only allows this device to perform counter tasks, such as edge counting. Digital input tasks (supported on devices such as the 6528) are used to take a snapshot of a line (ie read its high or low value), while counter tasks can only detect rising or falling edges. That being said, it would be possible to determine the state of a digital line using this device, but it would require you to write a software algorithm to perform the "read".
If you know the default state of the line (all pulled low on this device) you could use the counter functions to detect a rising edge, and then you would know that the line is high. Conversely, if the line was currently high, you could set up a different task to detect falling edges to know when the line was low.
Although this is possible, I would suggest using a DIO card to perform these tasks. Please let me know if you have any additional questions...
Nicholas B, National Instruments