National Instruments SCXI-1129 User Manual
Also see for SCXI-1129: Getting started guideGetting started guideGetting started guideUser manualUser manual
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Contents
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Chapter 2 Using the SCXI-1129© National Instruments Corporation 2-21 SCXI-1129 User Manualan SCXI-1129 with external instruments to guarantee that both themeasurement instrument and the matrix have settled before taking thenext measurement.The second type of scanning, software scanning, is a method by whichmatrix connections are initiated through the software. This method requiresno trigger connections. Software scanning does not offer the time accuracyof hardware-timed scanning.Hardware-Timed ScanningIn hardware-timed scanning, the software downloads a list of commandsto the SCXI-1129. The software then starts executing the scan list. Thescan list executes until reaching a wait for a trigger command. When theSCXI-1129 receives a trigger, the scan list continues to advance untilreceiving another wait for trigger command. Between waiting for triggers,the switch state of the matrix can be changed. When the matrix haschanged state, the scan list can be instructed to send a Scanner Advanced(SCANADVD) signal to the measurement instrument indicating thatthe system is ready for another measurement to be made.Hardware-Timed Scanning Using a DMMWhen using a DMM to control a chassis, synchronous mode is the onlymode in which the DMM and the SCXI-1129 can operate. The DMMissues a trigger to change the matrix configuration at regular intervals. Youcan program the interval at which the DMM sends triggers; set the intervalas follows.where n is the number of activated switches.The module that connects directly to the DMM is referred to as the cabledmodule. If more SCXI-1129 modules are added to your system, the triggeris bused over the SCXI backplane allowing other modules to be triggered,as shown in Figure 2-14. These additional modules are referred to asnon-cabled modules since they do not require you to cable the DMMdirectly to them.n 352 μs× n 1–3------------ 4 ms( ) debounce time+ + |
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