Digital Input with NI DAQmx using Matlab

[ajn3000]

Hi,

i'm having a problem reading the digital input functions from NI-DAQmx in MATLAB (using calllib functions from the DLL).

I use the  NI USB-6251 BNC device.

So, i want to read 4 digital pins (0..3) and stop reading until one of these pins are set HIGH.

To do this, i'm going this way:

   1. create DI task

   2. create DI channel

   3. in a while-loop, use the  DAQmxReadDigitalU32 function to read the digital values.

but that doesn't work. i also tried triggering and timing, but it's always the same thing:

I don't get any values (just zeroes), even if all pins have a 5V input. The pvalues1 variable also returns 0, which means that no values have been read.

Digital output and analog input/output works fine!

Did i make a mistake in the source code? I couldn't find any useful information on the NI homepage or on google about digital input in Matlab or ANSI C.

 
can anybody help me?

Thanks!

    Jan P.

Here's my source code:

 

function [ReadHandle, values] = NI_Start_DITask(values)

DAQmx_Val_ChanForAllLines = 1;
DAQmx_Val_FiniteSamps = 10178;
DAQmx_Val_GroupByChannel = 0;
DAQmx_Val_ChanPerLine = 0;
DAQmx_Val_Rising=int32(10280);          
DAQmx_Val_Falling=int32(10171);
DIPtr=libpointer('uint32Ptr', 0);

%int32 DAQmxCreateDIChan (TaskHandle taskHandle, const char lines[], const
%char nameToAssignToLines[], int32 lineGrouping);

[a,b,DIPtr] = calllib('myni','DAQmxCreateTask','',DIPtr); % create task
DIPtr=libpointer('uint32Ptr',DIPtr);
b = calllib('myni','DAQmxCreateDIChan',get(DIPtr,'Value'),'Dev1/port0/line0:3','', ...
    DAQmx_Val_ChanForAllLines);                           % create DI channel
d = calllib('myni','DAQmxStartTask',DIPtr);

ReadHandle = DIPtr;

 

and then in the main function

...

values = zeros(1,1000);
p1=0;

vptr=libpointer('uint32Ptr', values);
pvalues1 = libpointer('int32Ptr',p1);
[ReadHandle, values] = NI_Start_DITask(values);   % open function above
pv = libpointer('uint32Ptr', 0);

while 1
    calllib('myni','DAQmxReadDigitalU32',ReadHandle,10,10,0,values,4000,...
    pvalues1,0);
    p1 
    values
    if pv.Value==1
        break
    elseif any(values)
         break  
    end   
    drawnow
end

NI_stopAndClearTask(ReadHandle);
NI_ResetHW('Dev1');
 

Message Edited by ajn3000 on 12-01-2009 01:37 PM

Message Edited by ajn3000 on 12-01-2009 01:37 PM

[ajn3000]

i forgot to mention that i get the error code -200088 when i create the DI channel.

i tried adding the "DAQmxIsTaskDone" between creating the task and creating the DI channel, but that function returns the same error code,

even if i use a zero-pointer when opening the DAQmxIsTaskDone function.

[ajn3000]

problem solved.

[lapislazuli]

How did you solve it?

[nathancolorado]

I'm getting the same error (-200088) whenever I try to add any channels. How did you fix it?

[nathancolorado]

I finally got it working - no more error -200088 for me!

I had to pass the initial task handle as empty - uint32([]). This is different from code here. This is the code that worked for me:

taskhDO0 = [];
[err,b,taskhDO0] = calllib('myni','DAQmxCreateTask','DO0',uint32(taskhDO0))
[err,b,c,d] = calllib('myni','DAQmxCreateDOChan',taskhDO0,'Dev1/port0/line0','',DAQmx_Val_ChanPerLine)

I am using matlab 7.8.0 (R2009a) on XP. 

[lid]

---

nathancolorado wrote:

I finally got it working - no more error -200088 for me!

I had to pass the initial task handle as empty - uint32([]). This is different from code here. This is the code that worked for me:

taskhDO0 = [];
[err,b,taskhDO0] = calllib('myni','DAQmxCreateTask','DO0',uint32(taskhDO0))
[err,b,c,d] = calllib('myni','DAQmxCreateDOChan',taskhDO0,'Dev1/port0/line0','',DAQmx_Val_ChanPerLine)

I am using matlab 7.8.0 (R2009a) on XP. 

---

 

 Odd, when I tried that I got error -200604 ("NULL pointer was passed for a required parameter.") when creating the task. I'm running MATLAB R2009b 32-bit on Win 7 32-bit, NI-DAQmx 9.1.0.

 

 

Message Edited by lid on 06-01-2010 07:17 PM

[nathancolorado]

The code that works for me is posted here.

[lid]

---

nathancolorado wrote:
The code that works for me is posted here.

---

Thanks for the reply! Using that code, I get: 

??? Error using ==> DAQmxCheckError at 24

DAQmx error - NULL pointer was passed for a required parameter.

Error in ==> DAQmxCreateDOChan at 28

DAQmxCheckError(lib,err); 

[lid]

---

nathancolorado wrote:
The code that works for me is posted here.

---

Also, which version of NI-DAQmx are you using? Thanks!