I got some time to test the setup using NMOS FETs. Here is the circuit that works. Resistor values aren't terribly important. What I found is that after RUN is raised, the Flash memory /CS pin must be held low for 5 mS to give the RP2350 time to finish sampling it. So, the sequence to force the RP2350 into BOOTSEL mode is as follows:Note that the _TRIG signals are inverted from the voltage values at the chip pins.
The length of the Q2, R5, R4, /CS connection needed to be short. 10 cm, did not work. 5 cm did. Also, Gnd connections needs to be similarly short.
Code:
Raise BOOT_TRIGRaise RUN_TRIGwait 10 mS // could be shorterLower RUN_TRIGwait 5 mS // absolute minimumLower BOOT_TRIGThe length of the Q2, R5, R4, /CS connection needed to be short. 10 cm, did not work. 5 cm did. Also, Gnd connections needs to be similarly short.
Statistics: Posted by phil from seattle — Thu May 01, 2025 9:37 pm