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What are the scanning options for the SCXI-1127/1128 Switch Module?

Hardware: SCXI>>Modules>>SCXI-1127

Problem:
I have an 1127/1128 Switch module and I am trying to do a scanning operation with a National Instruments DMM, what options do I have?

Solution:
You have two options for scanning the SCXI-1127/1128; Synchronous scanning and Handshaking.

Synchronous:
In synchronous scanning, each entry in the scan list is executed after the switch receives a digital pulse (trigger input) from the DMM. The DMM is programmed to take measurements at regular intervals and to generate a digital pulse after each measurement. When the switch receives this digital pulse, it advances to the next entry in its scan list. You must program the DMM interval time to account for the time required by the switch to activate and settle.

Hardware and Software Configurations for Synchronous Scanning

If you are using the SH9MD-AUX cable to communicate with SCXI switches (DMM is controlling the switch using the same cable), set Trigger Input to Rear Connector in niSwitch Configure Trigger. Also set Measurement Complete Destination to External in niDMM Configure Measurement.
If you are using the AUX trigger Cable to exchange triggers between the DMM and the switch (the DMM is not controlling the switch. IT is controlled by another device), set Trigger Input to Front Connector in niswitch configure Trigger. Also set Measurement Complete Destination to External in niDMM Configure Measurement.
If you are using a PXI DMM in the rightmost slot of the PXI/SCXI combination chassis, you can send the MC signal to the SCXI switches through the internal PXI/SCXI lines. Set Trigger Input to TTL0 in niSwitch Configure Trigger.
- With NI 4060 set Measurement Complete Destination to TTL0 in niDMM Configure Measurement Complete Destination to send the MC signal to SCXI TRIG0.
- With NI 4070 set Measurement Complete Destination to LBR_TRIG0 in niDMM Configure Measurement Complete Destination to send the MC signal to SCXI TRIG0.

Handshaking:
Handshaking is very similar to synchronous scanning except that the switch sends a digital pulse (Scan Advanced Output) back to the DMM after each set of connections. Instead of taking measurements at regular intervals, the DMM is triggered by the digital pulse from the switch. The DMM needs to be initialized and ready to accept a trigger for its first measurement. The switch is then initialized, executes its first entry in the scan list, waits for a digital pulse (Trigger Input) to execute its next entry, and generates a digital pulse (Scan Advanced Output). When the DMM receives Scan Advanced Output, it takes the first measurement and generates a Trigger Input signal. When the switch receives Trigger Input, it executes the next entry in the scan list, generates another Scan Advanced Output and so on. A common cabling scheme for handshaking is to connect the trigger output of the DMM to the Trigger Input of the switch and to connect the input trigger of the DMM to the Scan Advanced Output of the switch.

Hardware and Software Configurations for Handshaking

If you are using the AUX Trigger Cable to exchange triggers between the switch and the DMM (you cannot handshake through the backplane of a PXI/SCXI combo chassis.):
- Set Trigger Input to Front Connector in niSwitch configure Trigger for SCXI switches.
- Set Scan Advanced Output to Front Connector in niSwitch configure Trigger for SCXI switches and to External for PXI switches.
- Set Measurement Complete Destination to External in niDMM Configure Measurement Complete Destination.
- Set Trigger Source to External in niDMM Configure Trigger.
- Set Sample Trigger Source to External in niDMM Configure Multi Point.

Report Date: 08/20/2003
Last Updated: 12/12/2008
Document ID: 30J9TOZO

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