Problem with USB AVR programmer firmware update

I am trying to update my Pololu USB AVR programmer firmware from version 1.01 to 1.04.
But I am trying some problems with it. I can only get as far as getting the “FWBOOTLOAD” reply on the terminal.
After that, the yellow LED didn’t come on, and when I typed “s” into the terminal, the reply was “??”. If I just press Enter after “FWBOOTLOAD”, I get “?” as replies.
Please help me to update the firmware.
Thank you.

Hello. I am sorry you are having trouble. Pressing enter is not part of the procedure, so please try again without pressing enter.


I followed the procedure strictly. The manual says the yellow LED would come on after getting “FWBOOTLOAD” on the terminal, but mine did not do that. I typed in “s” as per the manual anyway, and then got “??” back. So my diagnosis is that when the terminal was showing “FWBOOTLOAD”, the unit didn’t go into the state which it was suppose to be in for the “s” command to work. Please help. I am a big fan of Pololu products.

Hello, Bob.

If you send just “fwbootload” to the bootloader, that should get it in to the state where the yellow LED turns on. However, if you send an invalid character after that, such as a new line or carriage return, then the bootloader will return to its initial state and the yellow LED will turn off. That’s why it is important to not press enter and to use a terminal program that allows you to send characters without sending newlines. What terminal program are you using?


I am using Putty.
I completed the update. Turns out I had to set the Local Line Editing option to Auto, because I set it to Force on before. I think this option allows me to type in all the characters I want to send in the terminal before sending them. When I had this option set to force on, I had to press enter to send the characters I typed in. But I still got the right reply characters which is “FWBOOTLOAD”. Anyway, thanks.

I’m glad you got it working.

When the bootloader received “fwbootload” it would have sent back FWBOOTLOAD and turned the yellow LED on, but PuTTY must have sent a newline character immediately afterwards that caused the yellow LED to turn off (that newline would generate no response character from the bootloader, but it would put the bootloader back in to its initial state). Then when you sent “s”, the bootloader was expecting “f” so it sent back a “?”. Then when you sent a newline character, the bootloader was still expected “f” so it send back the second question mark.