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Target communication errors using Dynamic C with Windows 7

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Problem Resolution

While having an issue with really slow performance on some test fixture’s FTDI USB-to-serial COM ports, we discovered that in the USB COM port’s “Advanced Settings” dialog box there is a “Latency Timer (msec)” selection drop-list. It was found that reducing the latency setting from the (apparent) default of 16 msec to a much smaller value (1 or 2 or 3 msec) resulted in much better performance.

If a customer is having lots of problems with frequent target communication errors when using DC 9.62 on a Windows 7 x64 PC, try setting 1 to 3 msec latency on the COM port that is used with DC 9.62. To do this, take the following steps:

Go to the FTDI USB-to-serial COM port “Advanced Settings” dialog box.
Notice in the “BM Options” area the “Latency Timer” selection drop-list.
Change this setting to a number from 1 to 3 msec.

The latency setting of 1 msec might be using up more CPU and / or USB bandwidth than necessary, so it might be best to experiment a little and use the highest latency setting that doesn’t cause frequent TC errors.
This tip might be handy for customers using DC 9 and (probably) earlier DC versions.



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