NI 9476 - is whole port refreshed after writing only one bit?

[grega]

Hello,

I am using a combination of NI 9476 and NI 9425 in a cDAQ 9188 housing to control a linear motor via a parallel cable.

I have some problems with the motor and I would like to rule out a potential problem with cDAQ.

If I have a task for one bit in labview (specifically for NI 9476 module) and I this one bit in labview, is the whole port refreshed (old values are re-written and new values are newly written) or only that bit?

So to rephrase, if I put bit1 high, and then independently I put bit2 high (both bits are a part of port0), is the whole port refreshed with old/new values?

Thanks,

Regards...

[BalazsNagy]

Hi grega!

So you have for example two tasks, were you write two digital lines independently, and you write the P0.1 with the second task after you wrote the P0.0 with the first task.

The value of the P0.0 will be the value, you set in the first task, even if you write any other values to other lines in the same port.

(Actually if you kill the task, and do not change the state, it will remain for example true.)

To tell the truth I don't know exactly how does the refreshing of the state of a line, that was set previously occurs when you set the state of an other line.

Do you have any problems with this? Did you measure something strange? (Or why is this important for your project?) 

Best regards,

[grega]

Hey Balazs,

yes, exactly. I am wondering how the hardware refreshes ports or lines. So if I change only one line, does the hardware refresh the whole port or only a single line (not in a software sense...that I know)?

The thing is that I am using a motor and have its input bits tied to a NI 9476 module. When I want to drive the motor I change only one bit. But if the whole port is "refreshed", the motor controller responds to "new" values, eventhough they are the same as "old" ones, and re-initializes the encoder, which takes about one second. As I said, I am not yet certain about the source of the problem, I just want to rule out this possibility. I am also getting a new motor driver to test it, if there is something wrong with the old one...

Kind Regards

[grega]

I got another controller with encoder and the situation is the same, so now I need to start to worry. Does anybody have any ideas of how labview refreshes lines/ports??

Best Regards

[grega]

Problem solved, but thank you anyways...

Regards