Chapter 9 SCXI—Signal Conditioning

Parallel Mode for Digital Modules

When you operate a digital module in parallel mode, the digital lines on your DAQ device directly drive the individual digital channels on your SCXI module. You must cable a DAQ device directly to every module operated in parallel mode.

You may want to use parallel mode instead of multiplexed mode for faster updating or reading of the SCXI digital channels. For the fastest performance in parallel mode, you can use the appropriate onboard port numbers instead of the SCXI channel string syntax in the digital VIs.

Note If you are using a 6507/6508 (DIO-96) or an AT-MIO-16DE-10 device, you also can operate a digital module in parallel mode using the digital ports on the second half of the NB5 or R1005050 ribbon cable (lines 51–100). Therefore, the DIO-96 can operate two digital modules in parallel mode, one module using the first half of the ribbon cable (lines 1–50), and another module using the second half of the ribbon cable (lines 51–100).

SCXI Software Installation and Configuration

After you assemble your SCXI system, you must run Measurement & Automation Explorer or the configuration utility to enter your SCXI configuration. LabVIEW needs the configuration information to program your SCXI system correctly.

Special Programming Considerations for SCXI

When you want LabVIEW to acquire data from SCXI analog input channels, you use the analog input VIs in the same way that you acquire data from onboard channels. You also read and write to your SCXI relays and digital channels using the digital VIs in the same way that you read and write to onboard digital channels. You can write voltages to your SCXI analog output channels using the analog output VIs. The following sections describe special programming considerations for SCXI in LabVIEW, including channel addressing, gains (limit settings), and settling time.

Note This section does not apply if you use the DAQ Channel Wizard to configure your channels. On Windows, the DAQ Channel Wizard is part of Measurement & Automation Explorer. If you use the DAQ Channel Wizard, you

address SCXI channels the same way you address onboard channels—by specifying the channel name(s). LabVIEW configures your hardware by selecting the best input limits and gain for the named channel based on the channel configuration.

Chapter 9 SCXI—Signal Conditioning

SCXI Channel Addressing

If you operate a module in parallel mode, you can specify an SCXI channel either by specifying the corresponding onboard channels or by using the SCXI channel syntax described in this section. If you operate the modules in multiplexed mode, you must use the SCXI channel syntax.

An SCXI channel number has four parts: the onboard channel (optional), the chassis ID, the module number, and the module channel.

In the following table of examples, x is any chassis ID, y is any module number, a is any module channel, and b is any module channel greater than a. z is the onboard channel from which the conditioned data is retrieved. If you operate in multiplexed mode, analog input channel 0 reads the data from the first cabled chassis. If you use VXI-SC submodules, LabVIEW ignores the onboard channel, because VXI-DAQ provides a special channel for retrieving data from submodules.

The channel input for DAQ VIs is either a string (with the Easy I/O VIs) or an array of strings. Each string value can list the channels for only one module. With the array structure for channel values, you can list the channels for several modules. Therefore, for one scanning operation, you can scan several modules. You can scan an arbitrary number of channels for each module, but you must scan the channels of each module in consecutive, ascending order.

Note You do not need the SCXI channel string syntax to access channels on the SCXI-1200 module. Use 0 for channel 0, 1 for channel 1, and so on. The SCXI-1200 module is identified by its logical device number.