Intermittant uploads via Serial bootloader

roger239955_stm1 · ‎2014-11-23

Posted on November 24, 2014 at 01:16

First excuse this newbee post, as this question has probably been asked before, but I've not found an answer.

I'm evaluating a several STMF103 based minimum development boards from eBay, and I'm getting a lot of problems putting the boards into Serial Bootloader mode, connecting via STMs windows ''demonstration'' uploader.

I'm using an external USB to serial (I've tried several different devices and none was better than the others).

The most problematic board I have uses a STM32F103RCT, and this only seems to enter bootloader mode immediately after power up. And even then only 50% of the time.

I've looked at all the connections and have hard wired Boot0 high and Boot1 low, and replaced the reset switch etc, to no avail.

Is there anything else that could cause the device to not enter serial bootloader mode?

From what I understand, in this mode, even the external clock crystal is not being used, but I'm not sure if my understanding of this is correct.

Is there anything else that causes these devices not to enter bootloader mode?

e.g. values on other pins, possibly clock problems, supply noise problems etc etc ????

Thanks again.

Roger Clark

Tesla DeLorean · ‎2014-11-23

Posted on November 24, 2014 at 03:20

The part starts and runs from the HSI clock. It is wait to see an 0x7F byte sent with 8E1 (8 bit EVEN parity, one stop)

It's not trying to receive 0x7F, but measure the timing, and program that into the baud rate register. If it sees some garbage or glitchy character is going to attempt to sync to that.

Cheap USB-to-Serial devices are notoriously unstable. Use a box with an on-board serial port, if you have such.

If you don't get the 0x79 response to the 0x7F, they yes you'd probably want to reset and start over.

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roger239955_stm1 · ‎2014-11-23

Posted on November 24, 2014 at 04:38

Thanks clive1

I will take a look try sending 7F from a terminal emulator and see what code I get back, I will also attach an oscilloscope to RX and TX and look to see how clean the signals are.

I have read that pull-ups are required on RX and TX but I'm not sure whether this is implemented on the board I am having problems with, because it didnt come with a schematic

Thanks again

Roger