In my experience, all of the metal dongles have the SWIM_RST pin exposed, not T_NRST (there are notes floating around from people complaining the RST doesn't work in SWD/JTAG mode, because of this).RogerClark wrote:It could be that RST is SWIM_RST, in which case its not a problem because UART can be on PB6 and PB7, but if RST means T_NRST that appears to be on another pin
I don't think I've run into that before - loopback works fine on the dongle I tested, but there are lots of variants out there (I even found a metal dongle with an F103 instead of an F101).RogerClark wrote:The other problem seems to be the pullup and series resistors, as it prevents serial loopback working.
Here are my notes from the last time I opened one up and probed the pins:
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From left to right, GND, 5V, SWDIO, SWCLK, with GND nearest the USB connector. PB6 is connected to TGT-RST (40ohms) PB13 is connected to TGT-SWCLK (40ohms) PB14 is connected to TGT-SWDIO (40 ohms) PB11 is connected to TGT-SWIM (40 ohms) PB5 is connected to PB6 through a 220 ohm resistor. PB12 is connected to PB14 through a 100 ohm resistor PB10 is connected to PB11 through a 220 ohm resistor PA5 is connected to PB13 Permanent 1.5k pull-up from USB D+ to 3.3V PA9 connected to blue LED through 1.5k resistor red LED conected directly to SWCLK or SWDIO, active low