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Chapter 3 Software Overview

NI-DAQ User Manual for PC Compatibles 3-120 ni.com

When you are using the SCXI-1200 to acquire the data, pass channel 0 to

the

Lab_ISCAN

functions; the SCXI Slot 0 takes care of all the channel

switching.

Building Analog Input Applications in Parallel Mode

When you operate the SCXI-1120/D, SCXI-1121, SCXI-1125,

SCXI-1126, SCXI-1141, SCXI-1142, and SCXI-1143 modules in parallel

mode, you need no further SCXI function calls beyond those shown in

Figure 3-43 to set up the modules for analog input operations. After you

have initialized and reset the SCXI chassis and modules, you can use the

DAQ

SCAN

,or

Lab_ISCAN

functions with the DAQ device. Remember

that the channel and gain parameters of the

DAQ

SCAN

,and

Lab_ISCAN

functions refer to the DAQ device channels and gains.

For example, to acquire a single reading from channel 0 on the module,

call the

AI_Read

function with the channel parameter set to 0. The

gain parameter refers to the DAQ device gain. You then can use the

SCXI_Scale

function to convert the binary reading to a voltage. The

AI_VRead

function call is not generally useful in SCXI applications

because it does not take into account the gain applied at the SCXI module

when scaling the binary reading.

To build a channel-scanning application using the SCXI-1120/D,

SCXI-1121, SCXI-1125, SCXI-1126, SCXI-1141, SCXI-1142, or

SCXI-1143 in parallel mode, use the

SCAN

and

Lab_ISCAN

functions to

scan the channels on the DAQ device that correspond to channels on the

module you want. For example, to scan channels 0, 1, and 3 on the module

using an MIO-16 device, call the

SCAN_Op

function with the channel

vector set to {0, 1, 3}. The gain vector should contain the MIO and AI

device channel gains. After the data is acquired, you can demultiplex

it and send the data for each channel to the

DAQ_VScale

function.

Remember to pass the total gain to the

DAQ_VScale

function to obtain

the voltage read at the module input.

In many of the data acquisition function descriptions in the NI-DAQ

Function Reference Online Help file, the count parameter descriptions

specify that count must be an integer multiple of the total number of

channels scanned. In channel-scanning acquisitions in parallel mode,

the total number of channels scanned is the numChans parameter in

the

SCAN_Setup

SCAN_Op

SCAN_to_Disk

Lab_ISCAN_Start

Lab_ISCAN_Op

,or

Lab_ISCAN_to_Disk

function calls.