MATLAB: Do I receive an error while using the GETDATA function with the Data Acquisition Toolbox 2.5.1 (R14SP1)

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I am able to successfully set up and start my analog input device. When I attempt to access the device using the GETDATA function, I receive the following error:

 internal GETDATA error: Trigger start not in buffer

After this error, the SamplesAvailable property of my device decreases, but not by the amount I specify with GETDATA. I am able to view the results using PEEKDATA.

Best Answer

This bug has been fixed in Release 14 Service Pack 3 (R14SP3). For previous product releases, read below for any possible workarounds:

We have verified this as a bug in the Data Acquisition Toolbox 2.5.1 (R14SP1) in the way the engine works with an external clock. When working with an external clock, the engine sometimes makes errors in determining when a particular hardware trigger took place.

When a device is operating with external clocking, it is hard for the software to determine when a trigger or a sample occurred. The toolbox uses the SampleRate property to estimate when a sample or trigger occurred. To work around this issue, set the SampleRate property to a value equal or greater than the external clock rate.

Related Solutions

MATLAB: Does the ANALOGINPUT object not acquire any data when I use an external trigger provided by a DIGITALIO object using Data Acquisition Toolbox 2.14 (R2009a)

The use of an external hardware trigger using Digital Signal source is specified by setting the "TriggerType" property to "HWDigital". When doing so, the condition which initiates the data acquisition is controlled by the "TriggerCondition" property. For National Instruments boards, this value is by default set to "NegativeEdge" i.e. the trigger occurs when the negative (falling) edge of a digital signal is detected.

In the code snippet above, only a rising edge occurs when you write a value "1" to the DIGITALIO line. Hence, as no trigger is received, no data will be acquired which results in the call to the GETDATA function timing out.

To ensure that data has been acquired, you can use one of the following methods:

1. Set the "TriggerCondition" property to "PositiveEdge" or

2. Generate a negative edge on the trigger signal by using the following code snippet:

putvalue(dio, 1);
start([ai ao]);
putvalue(dio, 0);

MATLAB: Am I unable to trigger the data acquisition device when I set the “TriggerType” property to “HwDigital”

This change has been incorporated into the documentation in Data Acquisition Toolbox 2.15 (R2009b). For previous releases, read below for any additional information:

For data acquisition objects created using NI-DAQ, there is an additional device specific property called as "HwDigitalTriggerSource" which has to be set when the "TriggerType" property is set to "HwDigital".

"HwDigitalTriggerSource" defines which pin is used to initiate a data acquisition when the "TriggerType" property is set to "HwDigital".

ai = analoginput('nidaq','Dev1');
addchannel(ai,0);
set(ai,'TriggerType','HwDigital')
set(ai,'HWDigitalTriggerSource','PFI0');

"HwDigitalTriggerSource" can take values from PFI0 to PFI9 or RTSI0 to RTSI6.

(Consult the manual for the specific pin of the board being used)

Please note that the "HWDigitalTriggerSource" property is only implemented for the Analog Input object and not for the Analog Output object.

Best Answer

Related Solutions

MATLAB: Does the ANALOGINPUT object not acquire any data when I use an external trigger provided by a DIGITALIO object using Data Acquisition Toolbox 2.14 (R2009a)

MATLAB: Am I unable to trigger the data acquisition device when I set the “TriggerType” property to “HwDigital”

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