Accessing the Unused AI Channels of a DAQ Card If a SCXI Chassis Is Connected

Updated Nov 28, 2018

Reported In


  • SCXI-1000
  • PXI-6259


  • NI-DAQmx

Issue Details

I have an M Series DAQ card that has two connectors on the front. I have an SCXI chassis connected to connector 0 and I wanted to know if I can use the analog input channels that are listed in connector 1 in my application. Is this possible?


When driving a SCXI chassis in multiplexed mode, all the Analog Input Data is being multiplexed over Analog Input Channel 0. You can access the unused and unreserved I/O lines of your DAQ board. You can acquire data on the channels that are listed in the second connector of the DAQ card. In case that you have only one connector (or port) in your DAQ card, you can use the SCXI-1180 to bring the channels and lines signals through to the SCXI chassis front panel.

In case that you want to run different DAQmx task simultaneously, you have to keep in mind the number of timing engines available on your card. Refer to the Related Links section below for further information about this topic.  

Additional Information

Reserved Analog Input Channels
This section applies only to SCXI systems used with a plug-in DAQ board or PCIMCIA card.

When using analog input modules in multiplexed mode in a single chassis, the analog input channels of all of the SCXI modules in the chassis are multiplexed to a single analog input channel of the DAQ board. In general, the remaining analog input channels of the DAQ board are available for other uses. However, if your SCXI cable assembly connects your DAQ board to a SCXI module that has parallel mode capabilities, the analog input channels of your DAQ board that would have been used to drive the module in parallel mode will be unavailable even if you use the module in multiplexed mode. 

For example, if you cable the DAQ board to an SCXI-1120, SCXI-1140, or SCXI-1141, the module drives eight analog input channels in parallel of the DAQ board, so these lines are unavailable. If you cable your DAQ board to an SCXI-1100, SCXI-1102, or SCXI-1122, which do not have parallel output capability, only one analog input channel of the DAQ board is used, regardless of which other modules are in the chassis. Reference the manual before setting up your SCXI system in parallel mode in order to understand exactly how your module will behave in this mode. 


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