NI PXI-6528 programming

[mrbean]

Although this code is not yet complete (I'm not actually comparing out/in), the thing I really want to do, once I prove the concept with the looping construct, is to change the granularity such that I can click on a data out 'bit' and 'write' that bit to the input.  Any thoughts?

[Yardov]

Hi Mr. Bean,

Just to add to this thread a couple of very good resources:
1. Once you create the DAQ assistant express VI, you can right click and convert it to DAQmx code. This will help you control each line and the data type will be correct already.
2. There is a NEW great documentation about DAQmx that through video and text tutorials, this series will take the you from verifying your device's operation in Measurement & Automation Explorer (MAX) to programming data acquisition applications using LabVIEW. It is intended for both the beginner who wants to learn how to use the DAQ Assistant, as well as the experienced user who wishes to take advantage of advanced NI-DAQmx functionality.

Hope this complements the thread,

[mrbean]

I looked at a number of examples and still have questions.  If I have a DAQmx Read (configured as a Digital 1D Bool Nch 1Sample), the only input it contains is the task.  So how do I specify which specific ch I want to read.  Or, am I (in this case) always reading all 24 channels that I set up in my task.

[Dennis_Knutson]

From the DAQmx FAQ :

Q: What is an NI-DAQmx task?

A: An NI-DAQmx task is a collection of one or more virtual channels with timing, triggering, and other properties. Conceptually, a task represents a measurement or generation you want to perform. You can set up and save the configuration information in a task and use the task in an application.

The channels are defined in MAX or with the DAQmx Create Virtual Channel. In order to change channels, you have to create a new task.

[mrbean]

I think the code generated by the DAQmx assistant created one task and assigned all 24 channels to the one task.  That's where I think the confusion is coming in.  In this scenario, if I understand you correctly, I will have no choice but to write to

all 24 channels everytime.  If I want one channel granularity, the task(s) must be created that way initially.  Is this correct?

[Dennis_Knutson]

The DAQ Assistant will create a task with whatever channels you selected. If you want a task with a single channel, only select the specific channel you want. In a nutshell, the answer is yes. In the original description of what you want to do, I'm sure why you would want to do anything other than all channels at once.

[mrbean]

As I stated at the beginning of this thread, my goal is write a test that 'walks a one' (in this case, a boolean true) through the 24 output pins of my DAQmx device and reads the written value at the appropriate (loopback) input pin.  I then want to create a different VI (or a version of the first)  that allows (if debug is needed) to write to any one output and verify the value made it to the input.

[Dennis_Knutson]

You seem to be missing the point. You can do it either way. There is the shipping example called Write Dig Chan. There the input is a Boolean Array. If you want, you can set it up so that the user can only select a single element to be true. An XControl is one way to do this. An event structure could also be used. You could also provide the user with the option to select a single channel and the logic state. I think there is an advantage to drive all lines to zero while you monitor all of the other lines at once. For example, if there is a short and when you drive output x, expect only input y to be high, and input z also goes high, you won't see this if the task only contains channels x and y.

[mrbean]

I ended up getting the code to work last week.  There was a test fixture wiring problem.  A question I have, though, is that it seems that the DAQmx Write only accepts an array of boolean as an input.  This worked out well, since I'm trying to write/read 24 I/O lines at one time.  Does DAQmx even let you write a number (non-boolean) to it?

[Dennis_Knutson]

Of course it allows you to write a number. You never looked at some of the shipping examples mentioned earlier (i.e. Write Dig Port). Do you also see that little box below the DAQmx Write? It's called the polymorphic VI Selector. Click on it and see all of the options you have for doing a digital DAQmx Write. Right clicking on the DAQmx Write and selecting 'Help' would work too.