General • Re: Problem with programming and debugging on SWD pins

It seems unlikely to me it would be a hardware issue if the same issue manifests itself for multiple people.

Looking at the Debug Probe schematic -It seems to me that, if GPIO12 were 3.3V and SWCLK were 0V, or GPIO12 were 0V and SWCLK were 3.3V, there would be 33mA sourced from or sunk by GPIO12. That would appear to be beyond the GPIO pad capabilities and could potentially permanently damage the GPIO pin.

Similarly if GPIO14 were 3.3V and SWDIO were 0V, or GPIO14 were 0V and SWDIO were 3.3V.

Given GPIO12 appears to have lost its pull-to-0V capability the most plausible explanation would be that GPIO12 was output low (0V), SWCLK was output high (3.3V), that the 33mA burned out the pull-to-0V circuitry.

How that could happen or come about I don't know. One possibility is the SWD connector on the Debug Probe was at some time inadvertently connected to the UART on the target board - Which also brings into question the similar circuitry used in the Debug Probe to connect to UART on the target.

As said, the first thing to do would be to check if GPIO12 can pull its output low, check whether the pull-to-0V circuitry has been burned out or not.

Statistics: Posted by hippy — Sat Jun 29, 2024 1:59 pm

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