Here is the proposed update:
1) selecting DTR for reset does the job, the s/w on the chip is clearly stopped and a reset is done
2) with the scope I can clearly see a) the reset signal and b) the repeated signal sent from the PC when trying to program
3) on the Rx (towards PC) I do not see any signal change at all, signal remains High
From what I understand from reading the MCS bootloader sourcecode - the bootloader should send some characters towards the PC as well [chr(bstatus)].
I have the impression that the micro takes much shorter time now between Reset and starting the program. Now it is about 3 sec, but I did not measure what it was before.
So I fear I have to get an ISP programmer, adapt it to the board (no ISP I/F foreseen on the PCB) and figure out how to inhibit the FT232R chip.
Cheers,
Johannes
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