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Multiplexer Expansion with NI Switch Executive

Primary Software: Switch Executive
Primary Software Version: 2.1
Primary Software Fixed Version: N/A
Secondary Software: N/A

Problem:
I need to create a multiplexer switching configuration that has more channels than any single multiplexer module available from National Instruments. Can I can achieve this goal using multiple switch modules and NI Switch Executive?

Solution:
Yes, the COM terminals of two or more multiplexer modules can be connected to increase the channel count of a multiplexer configuration. However, it is very important that only one of the input channels on any of the modules is connected at any given time. Otherwise, the configuration is not truly a multiplexer and there is a risk of shorting input channels together and damaging hardware.

In order to guarantee that only a single channel on any of the modules is connected to the shared COM terminal, there must be exclusions defined in software. NI Switch Executive allows for software defined exclusions such as this, and makes this particular configuration, along with a variety of other custom configurations, simple to implement. Below are the steps needed to accomplish this:

1. Physically connect the COM terminals of all the switch modules that will be used for this configuration.
2. Create a new Switch Executive Virtual Device that includes the switch modules connected in the previous step.
3. On the "Hardwires/Buses" tab in Switch Executive, define a Hardwire between the COM terminals of each module that is part of this configuration.
4. On the "Channels/Exclusions" tab, define a mutual exclusion between all the input channels across all of the modules. To do this, simply click on the first input channel on the list of available channels and then shift+click on the last input channel to select all the channels across all modules. Then, click the associate button to add the selected channels to the mutual exclusion.

After these steps are completed, calls to this Switch Executive Virtual Device will only allow 1 channel across all modules to be connected to the shared COM terminal at any time, and a true multi-module multiplexer topology will be attained.

Related Links:
Product Page: NI Switch Executive

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Report Date: 09/25/2006
Last Updated: 10/27/2006
Document ID: 41ODDALA

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