NI 6224 digital output acting abnormal when PC power off.

[Anson840821]

Dear All,

I'm using NI 6224 to control cylinders, tower light and etc.

The output port just act abnormal during PC power off, and it go back to home position which it suppose to be when PC power on.

Is there any settings available in MAX be able to solve this?

Thanks.

[johnsold]

What do you consider abnormal behavior when the power is off?

Is this a PCI or PXI device? If it is PXI, what chassis and controller are you using?

Lynn

[Anson840821]

Before I turn off PC, all digital output is low.

After I turn off PC, all digital output change to high.

Its PCI card.

Thanks.

Anson

[johnsold · Accepted solution]

Anson,

The PCI card gets its power from the PC.  When the PC is off, the card has no power. With no power it is in an undefined state.  Most likely it presents a moderately high impedance to anything connected to its output.  If the external devices default to inputs = high when not actively pulled low (which is the case for TTL), then the power off state of the 6224 may look like logic high to the external devices.

There is no way that the PCI 6224 (or any other standard logic device) can control its outputs when it has no power.

If the external devices can still have power when the computer power is off, then you need to add some fail-safe circuitry between the digital outputs and the external devices.  The details depend on what the external devices require, how fast you need to disconnect, and other factors.

Lynn