Target Communications issues when using a USB programming cable with a Rabbit product and Windows 7

If you are using the USB cable, there may be an issue with the latency timer on your pc port.You might want to adjust the latency timer on the port you are using:

If you are having communications issue, you may need to adjust the latency timer on your port: (if you are using the USB programming cable)

There is 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. We found that reducing the latency setting from the (apparent) default of 16 msec to a much smaller value (1) resulted in much better performance.

Set 1 msec latency on the COM port used with DC 9.62.

We haven't had a DC 9.62 target communication error on that COM port since.

The FTDI USB-to-serial COM port “Advanced Settings” dialog box looks like:

Notice in the “BM Options” area the “Latency Timer” selection drop-list.

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.


If the USB drivers still do not install, you can get them from the FTDI website.


To locate the drivers you want to install for a device, select which of the driver types you wish to use (VCP or D2XX) and then locate the appropriate operating systems.

Select D2XX

You need to scroll down to select the one for your laptop.

Last updated: Jun 11, 2019

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