Chapter2 NI2590/2591 Operation
NI2590/2591 User Man ual 2-6 ni.com
Switch Control Circuitry
The switch control circuitry (SCC) is responsible for opening and closing
relayson the NI 2590/2591.You can load commands for the SCC into scan
memory using the driver software you receivedwith your kit. Consult the
onlinehelp or your software documen tation for specific information on the
appropriatecommands. There are two reasons for storing the commands in
memory before the SCC can process them:
•Both the operate and release times for the NI 2590/2591 are 15 ms.
Using memory storage, the software can send multiple commands to
the SCC without having to waitfor a r elay action to complete.
•The memoryi sused to store a scan list necessary for hardware
random scanning.
Random Scanning
The NI 2590/2591 can perform random scanning. In random scanning,
the switch module can open or close relaysin any order.
The scanl ist isd ownloadedto onboard mem ory.Commands in the scan
list can perform the followingactions:
•Openor close relays
•Waitfor an external trigger
•Generate a scanner advancedtrigger
•Generate a breakpoint interrupt
Youcan use the driver software to configure the switch module for
continuous or one-time scanning. In continuous scanning, the switch
module cyclest hrough the scan list until you disable scanning. For
one-timescannin g, the switch module runs through the scan list only once.
Youcan also use software commands to clear the scan list or reset it to the
beginningat any time.
The onboard control logic for the NI 2590/2591 switch module gives you
directaccess to open and close the relays, and also the ability to download
up to 1,024 random scanning instructions. The software included with the
moduleautomatically configures the NI 2590/2591and downloads the scan
listt oh ardwarefor you. The scan list itself downloads directly into the
memoryof the module to deliver the fastest scan possible with no controller