E series DIO initialized high during system startup

[graugnard]

In the thread "NI Discussion Forums : Most Active Hardware Boards : Multifunction DAQ : E-series digital lines status during sw initialization", in response to ElbaTech, reddog mentions that the DIO lines are pulled to high during initialization, since they default to inputs. For my process system, this is potentially very bad. After a power failure, the PC reboots, turning the DIO from outputs to inputs, sending the DIO to high, which activates my relays (SCC-RLY01) that are triggered by the DIO line. The relays open solenoid valves, which control chemical precursors. If the power fluctuates over night, I will have my chemicals flowing all night. Is there some way to configure the DIO channels to default to outputs? It doesn't really make sense to have a Normally Open relay connected to a DIO that will close the relay whenever the computer is restarted. I have a PCI-6036E with a SC-2345 attached to it. I use 4 DIO lines, each with a SCC-RLY01 relay, with solenoid lines connected to 2 and 3, then normally open connections.

Thanks,
Elton Graugnard

[LucaP.]

Hi Elton,

I want to clarify this situation.

I've copied this from the E-Series help manual:
"Power-On States of the PFI and DIO Lines
At system startup and reset, the hardware sets both the PFI and digital lines to high-impedance. This setting means that the device circuitry is not actively driving the output either high or low. However, these lines might have pull-up or pull-down resistors connected to them, as shown in the I/O Terminal Summary table in the specifications of each device. These resistors weakly pull the output to either a logic high or logic low state. For example, P0.0 is in the high-impedance state after startup, and the I/O Terminal Summary table shows that there is a 50 kΩ pull-up resistor. This pull-up resistor sets the P0.0 pin to a logic high when the output is in a high-impedance state."

The example which was described, is exactly what happens with the PCI-6036.

This KB shows a possible workaround: Setting the Default State of Digital Lines on E Series DAQ Boards

Hope this helps.