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USB - RS 485 - Strange

Discussion in 'SimTools compatible interfaces' started by Fahim, Jun 7, 2010.

  1. Fahim

    Fahim Member

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    I bought two standard usb rs485 adaptors from ebay for around 12 pound each.

    I had them plugged in USB slots COM3 & COM4 in my computor. My computer has 6 USB slots.

    I was getting actuator outputs of:

    40-62 outs per second, sometimes 80 outputs.

    I plugged the adaptors into COM5 & COM6 USB slots and all of the sudden:

    Out puts of 140-166 per second, sometimes showing 200 outputs.


    I dediced to use simxperience test range profile and do the test and keep the scn5 interface page open so i can see the outputs per second change as I'm moving the bars up on the test profiler.

    So as I'm moving the bars up and down and the outputs are going from 140 up to 160, then maybe down to 150, once (rarely this happens) sometimes flashing to 200 out puts per second.


    Anyway com 5 & 6 on my quad core makes the chips work better but are the outputs supposed to change always.
    Fahim, Jun 7, 2010
    #1
  2. bvillersjr

    bvillersjr Active Member

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    The updates will fluctuate when you are moving the slider. It is better (read more consistent) to gauge the performance of your adapters just after profiler startup. A well tuned adapter will provide 200-300 updates per second just after profiler startup and before pressing start or moving the sliders around.

    All of this being said, this reported number can be misleading. Just because X-Sim sees that you are sending 250 updates per second out to the virtual COM port, this does NOT mean that the virtual com port is flushing its buffer frequently enough to provide this level of performance.

    Most off the shelf adapters will buffer X-Sim's outputs into the USB buffer and flush the buffer out to the actuators when a certain buffer size is reached or when a time interval has elapsed.

    Many articles have been written in these forums on how to optimize the FTDI chip based adapters and most folks are able to achieve good update rates with them.
    bvillersjr, Jun 7, 2010
    #2