Serial at 115200 baud. I'm having problems with that, ok at 9600 though.

Added by DaveStyles over 10 years ago


I'm having problems with my PC talking to my mbed up at 115200, via teraterm when using the TEST firmware.
Luckily I now have a working eclipse environment in which I can change the firmware and recompile at will.

I've dropped down to 9600, recompiled and all seems ok. The only question is, was it 115200 for a reason ?

I only have those micro usb leads that are about 5 feet long around, so I think it's probably a lead problem, but just checking it wasn't that fast for a specific reason before I drop the speed on the real firmware.



Replies (1)

RE: Serial at 115200 baud. I'm having problems with that, ok at 9600 though. - Added by KalleP over 9 years ago

The short 1m USB cable that I think came with my MBED (or some other place) would not work to detect the mass storage drive. I used some other 2m long cable and the USB worked fine.

At first I did not get my serial debug to connect but Windows (and MACOS) need to install drivers from the MBED website. After that it was fine, sometimes garbage characters come through when first connecting to the USB serial port with terraterm.

Remember that serial OVER USB is moving the data at the FULL USB speeds of 2MB/s and only converts to NRZ ASYNCH when it leaves the USART at the other end (on the MBED magic chip I believe) so it can connect to the ARM serial port. Any speed connected effects on the serial link have to be occurring between the two ICs on the MBED module and not in the cable, the USB negotiation could not take place with a flaky or marginal cable.

A rare problem could surface if the characters cause host side interrupts at a speed faster than it can cope with but I don't think any modern PC could not keep up, they can stream video over USB these days. The ARM chip on the MBED could also have issues with the character rate but it seems unlikely that only you would experience it.

Johannesburg, South Africa