Reading digital line

[Grass_Pitch]

Hello All,
I am triggering data acquisition from the PCI-6036 counter based on the boolean value from either a switch on the front panel (software) or a foot-pedal connected to the DAQ board (which connects the board's +5 V to the digital line). Everything works as I want to to (that is I can use either the front panel control or the foot-pedal for data acquisition) except that when I initially start the Labview programme, the state is true on the digital line even if the foot-pedal is not pressed. Does anyone know what is the trouble?

In the stripped down example I have attached, you'll notice that the moment that you run the vi, the line state is on and after that the programme seems to work well.

Thanks,

Karthik.

[Scott_R]

Hello Karthik,

Thank you for contacting National Instruments. The digital input/output signals for the PCI 6036E default to the high state when no other value is being written to them. Internal to the board, there is a 50 KOhm pull-up resistor driving the line high. This can be overcome in two ways:

1) You can connect a 20 kOhm resistor from the terminal that you want to use to GND. This will cause the signal to be low until a voltage is applied to the digital line.

2) In your program, you can initialize the lines to a low state before any other code executes.

Try either of those methods to initialize the line states to low. If you have any further questions on this issue, let me know.

Regards,
Scott R.
Applications Engineer,
National Instr
uments