USB-to-Serial(product 391) max Baud Rates

I just finished installing the USB-to-Serial mini-board on my Windows XP machine and I’m only able to set the baud rate up to a maximum of 128k not the 921k baud rate as I expected and listed on the product page. Is this correct, or did I install the wrong driver? Also if this is correct, is this limitation the same for Linux as well as for the Mac?

Driver Date: 2/22/2007
Driver Version:



In what sense are you unable to use the product at 921k baud? It sounds like you are trying to set the baud rate using the device manager, but this setting typically has no effect on virtual COM ports, and the numbers you see there are not a reflection of the capabilities of the adapter. Rather, the software you use for communication (e.g. hyperterm, the Pololu Serial Transmitter, or your own custom code) specifies the baud rate used for that communication, and the adapter works at 921k baud (I’ve just tested it using an oscilloscope and the Pololu Serial Transmitter running on XP).

- Ben

Thanks for your reply.

I’m using Realterm to interface with the mini-board and it throws out an error when I pick a baud rate larger than 128K; I also see 128K as being the largest baud rate in the device manager. But, I will take in your feedback and try another application to see if I can achieve the maximum baud rates the device can supply.

I was successfully able to test the 921.6 kbps baud rate using a Labview application I wrote - so this works!

Unfortunately, on a couple of occasions the Pololu COM port would disappear from the Device Manager and I’d have to re-start my computer to re-gain access to it.

Thanks for the update. I’m surprised you had to restart your computer. Did you try unplugging and replugging in the adapter?

- Ben

I found out that when I disconnect and re-connect the USB-to-Serial device while running Labview, Labview holds onto to the last COM port utilized. In order to have the COM port released and available for use again, I need to completely close Labview then re-connect the USB-2-Serial device.

One of those stupid little things that wastes a lot of time and make you wonder if you’re stupid too. For what its worth, I hope this post is helpful to those from the future . . .