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Chapter 3 Software Overview

If any of the modules to be scanned are SSH modules, you must establish

the Track/Hold setup of each one. To synchronize multiple SSH modules,

you can configure the module that is receiving the Track/Hold control

signal to send the Track/Hold signal on the SCXIbus so that any other SSH

module can use it. The Track/Hold signal can be from either the DAQ

device counter or an external source.

The

SCXI_SCAN_Setup

call establishes the module scan list, which

NI-DAQ downloads to Slot 0. Each module is programmed for automatic

scanning starting at its given start channel. If you need the SCXIbus during

the scan to route the outputs of multiple modules, this function resolves any

contention. If you are using an SCXI-1200, you can include the SCXI-1200

in the module scan list.

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 multiplexed mode,

the total number of channels scanned is the sum of all the elements in the

numChans arrayinthe

SCXI_SCAN_Setup

function call.

If any of the modules in the module scan list are SCXI-1100,

SCXI-1102/B/C, VXI-SC-1102/B/C, SCXI-1122, SCXI-1125,

SCXI-1126, SCXI-1141, SCXI-1142, SCXI-1143, SCXI-1520,

SCXI-1530, SCXI-1531, or SCXI-1540 modules, you can use

SCXI_Set_Gain

to change the gain or range setting on each module.

You also can use the

SCXI_Configure_Filter

function for the

SCXI-1122, SCXI-1125, SCXI-1126, SCXI-1141, SCXI-1142, and

SCXI-1143, SCXI-1530, SCXI-1531, and the

SCXI_Set_Input_Mode

function for the SCXI-1122.

The

SCXI_MuxCtr_Setup

call synchronizes the module scan list with the

DAQ device or SCXI-1200 scan list. In most cases (especially when using

interval scanning), it is best to ensure that the number of samples NI-DAQ

takes in one pass through the module scan list is the same as the number

of samples NI-DAQ takes in one pass through the DAQ device scan list.

Please refer to the

SCXI_MuxCtr_Setup

function description in the

NI-DAQ Function Reference Online Help file.

After you have set up the SCXI chassis and modules, you can perform more

than one channel-scanning operation using the

SCAN

Lab_ISCAN

functions without reconfiguring the SCXI chassis or modules.