problem with INH output after power-on reset - PCI-7344

[Buechsenschuetz]

We hardly ever use the INH outputs (the lines are disconnected) but in one case we do. We have a drive which sometimes needs manual adjustment, so we have to turn off the torque, i.e. activate the INH output via software. This drive is part of an adjustment mechanism which should remain in a stable position even if our software is not running. Just recently we found that the INH line is activated immediately after starting the computer, i.e. the drive has no power. As soon as we start our software (using NI drivers etc) the INH line is de-activated and the drive performs as usual, i.e. it is powered. This is somewhat annoying since the drive always makes a minor jerk (due to the behaviour of the driver board when receiving a signal on the INH input) and the system needs re-adjustment. Usually the drive used to remain stable, i.e. the INH line was NOT activated after powering on the host computer. Have there been any recent changes to the "state after reset" of the 7344 outputs? We are now using driver versions 8.1 and Windows7, the firmware was updated some weeks ago. We are going to evaluate whether the boards behave differently with earlier software/Windows version but I just want to be sure whether there were any recent changes in the start-up procedure of PCI-7344. 

[Topper_Harley]

Hello Buechsenschuetz,

maybe this document is of any use for you:

Power-up state of the lines on the digital ports of the FlexMotion 7344 board

http://digital.ni.com/public.nsf/allkb/7D8CB525D5A011ED86256AEF0071E2ED?OpenDocument

Regards, Topp

[Buechsenschuetz]

Thank you for this hint, we have also found some information about setting the initial status of the digital I/O lines but our problem is the INH line of the motion control connector. In the meantime, we have found that this line will go to LOW state after powering up the host PC no matter how the initial state of this line is configured in MAX (and saved to flash, of course). It is possible to set the INH line such that it goes to a HIGH state when the NI drivers are loaded and our application software is not started yet. Anyhow, this does not solve our problem completely since any change of the INH status will cause minor movement of our drive. - As a workaround, we have set the driver board such that it is activated when the INH line is in LOW state. To pull the INH line to LOW state even when the host PC is switched off, we wire a /RES signal (connected to the +5VDC line of the DIG I/O connector) available in our system. As long as there is no power on this pin, the INH line to our driver board is pulled LOW. This solution requires a different configuration of our driver board and of the 7344 configuration but it seems the only possible solution. 

Thank you for that hint, we have found some information about the power-up status of the digital I/O but our problem is the INH line of the motion control connector.

[Topper_Harley]

Maybe these documents are helpful as well:

How to connect the 73xx inhibit and command signal outputs to third party drives

http://zone.ni.com/devzone/cda/tut/p/id/3442

Inhibit Output Signal Summary and Characteristics on NI Motion Controllers

http://digital.ni.com/public.nsf/allkb/619A2A562CD3188386257156004F7B1D?OpenDocument

Regards

[Buechsenschuetz]

We have found the second document before and the issues covered in the first one are quite clear to us, thank you anyway for your efforts. Our problem is that we need to maintain the same level on the INH line when the pc is switched off, when it powers up and when the NI drivers are loaded, there should not be any change of the status of this line to keep our drive from making unwanted moves (the motor driver board always goes to the full step status after an inhibit signal - since we are using microstepping this means that the drive may move from a "between full steps" position to a full step position). As mentioned, we are now trying to make a workaround by detecting the power status of the host pc and pulling the INH line low when there is no power on the pc. The active level of the INH line can be set to LOW or HIGH on our motor driver board. 

Message Edited by Buechsenschuetz on 04-30-2010 04:13 AM