Why Isn't Using "&" Performing Simultaneous Scanning?Hardware: Switches>>Multiplexer/Matrix>>PXI-2576
Problem: Normally when I use the ampersand (&) in my scan list, such as ch0->com0 & ch9->com1, my channels will connect simultaneously. On some switches (e.g. PXI-2576, SCXI-1127), it scans at the same rate as doing individual connections with ";" such as ch0->com0; ch9->com1. Why? Solution: The behavior of the "&" character is that it "Separates connect and/or disconnect actions. For example, the string ch0->com0 & ch9->com1 means connect CH0 to COM0 and CH9 to COM1 (in no particular order and with minimal delay)." (NI Switches Help - July 2008) While this normally means that connections occur simultaneously, it depends on the topology of the switch you are using. If you have a switch that is made of several smaller banks (e.g. PXI-2576), the switch's on-board chip sends the connection commands on a per-bank basis. This means that the connections on any given bank can occur simultaneously, but connection commands on different banks will occur sequentially. Some switch modules like the SCXI-1127 and SCXI-1128 do not support this simultaneous operation when they are in scanning mode. Because of this, in NI-SWITCH 1.5 and earlier, the "&" will be treated like a ";" (which prompts the switch to wait for the next trigger). For NI-SWITCH 1.6 or later, the "&" will produce the error message NISWITCH_INVALID_SCAN_LIST. You can see the Scan List entry of the NI Switches Help Document linked below for a discussion and examples of using "&" in a scan list. The NI Switches Help Document also installs on your computer with the NI-Switch driverRelated Links: Product Manuals: NI Switches Help (July 2008) Attachments:
Report Date: 02/07/2008 Last Updated: 10/13/2008 Document ID: 4I69OBD4 |
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