Is it possible to read digital data using an external clock (PCI-6259 M)?

[Magnus Wallblom]

I’m using a NI PCI-6259 M Series card and trying to write my program in VC++6.0 using the functions in the DAQmx driver.

Question1: Not all functions listed in the NI-DAQmx C Reference Help seems to be supported by my NI-card, where can I find information about which of the functions that are supported?

Question2: I want to read data from a device that clock out data on the falling edge of a clock signal. The clock signal and the data signal are routed to two DIO terminals on the NI-card. The question is if it is possible to read data using the clock as a sample clock? See two code examples below that doesn’t work. In both cases 10 samples are read at once, even if the external clock is not present.

Example 1

// Create tasks
Status = DAQmxCreateTask("", &m_ReadTrimTask);

// Set up read task
status = DAQmxCreateDIChan(m_ReadTrimTask, "Dev1/port2/line0", "", DAQmx_Val_ChanPerLine);
status = DAQmxCfgChangeDetectionTiming(m_ReadTrimTask,"Dev1/port2/line6","Dev1/port2/line6",DAQmx_Val_FiniteSamps, 10);

// Read data
int32 sampsPerChanRead, numBytesPerSamp;
status = DAQmxReadDigitalLines(m_ReadTrimTask, 10, 10.0, DAQmx_Val_GroupByChannel, result, 10, &sampsPerChanRead, &numBytesPerSamp ,NULL);


Example 2

// Create tasks
Status = DAQmxCreateTask("", &m_ReadTrimTask);

// Set up read task
status = DAQmxCreateDIChan(m_ReadTrimTask, "Dev1/port2/line0", "", DAQmx_Val_ChanPerLine);
status = DAQmxSetSampTimingType(m_ReadTrimTask, DAQmx_Val_SampClk);
status = DAQmxSetSampClkRate(m_ReadTrimTask, 1000.0);
status = DAQmxSetSampClkActiveEdge(m_ReadTrimTask, DAQmx_Val_Falling);
status = DAQmxSetSampClkSrc(m_ReadTrimTask, " Dev1/port2/line6");

// Read data
int32 sampsPerChanRead, numBytesPerSamp;
status = DAQmxReadDigitalLines(m_ReadTrimTask, 10, 10.0, DAQmx_Val_GroupByChannel, result, 10, &sampsPerChanRead, &numBytesPerSamp ,NULL);

[Sean_C.]

Hello Magnus,

Thank you for contacting National Instruments.

"Question1: Not all functions listed in the NI-DAQmx C Reference Help seems to be supported by my NI-card, where can I find information about which of the functions that are supported?"

The best place to look for this information would be the M Series Help Manual. There you can find the features of your PCI-6259 and what operations it supports.

"Question2: I want to read data from a device that clock out data on the falling edge of a clock signal. The clock signal and the data signal are routed to two DIO terminals on the NI-card. The question is if it is possible to read data using the clock as a sample clock? See two code examples below that doesn’t work. In both cases 10 samples are read at once, even if the external clock is not present."

Look at the "ContReadDigChan-ExtClk_Fn.c" example project which ships with the NI-DAQ driver. This is located at: C:\Program Files\National Instruments\NI-DAQ\Examples\DAQmx ANSI C\Digital\Read Values\Cont Read Dig Chan-Ext Clk.

You will have to make some minor modifications to convert this to a finite acquisition, but that is simply a matter of changing the "sampleMode" parameter of the DAQmxCfgSampClkTiming() function. You will also have to route your clock signal to a PFI line and specify which line in your code.

I hope this helps.

Sean C.
Applications Engineering
National Instruments