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Cannot put MCU into DFU mode #2

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opened 2025-07-27 16:36:56 -04:00 by molly · 0 comments
molly commented 2025-07-27 16:36:56 -04:00
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When programming the rev. 3 board for the first time I noticed it was really difficult to put the board into DFU mode.

I suspect this has something to do with the HWB pin not being at +5V when the reset is pulled low again. (or vice-versa?)

You basically have to get lucky with some of the keys in the bottom row of the keyboard that are connected to that pin.

The tricky part is, I don't want it going into DFU mode every-time the keyboard is reset. Perhaps I should solder in a programming switch that puts that pin high when I need to program. The switch can be unpopulated for production boards where the firmware will only be programmed once. If my friends want to re-program the board they can do the ol' bridge-two-pads/holes with a metal object trick.

I'll ruminate on this and a potential solution and figure out what to do for the next revision or sub-revision.

When programming the rev. 3 board for the first time I noticed it was really difficult to put the board into DFU mode. I suspect this has something to do with the HWB pin not being at +5V when the reset is pulled low again. (or vice-versa?) You basically have to get lucky with some of the keys in the bottom row of the keyboard that are connected to that pin. The tricky part is, I don't want it going into DFU mode every-time the keyboard is reset. Perhaps I should solder in a programming switch that puts that pin high when I need to program. The switch can be unpopulated for production boards where the firmware will only be programmed once. If my friends want to re-program the board they can do the ol' bridge-two-pads/holes with a metal object trick. I'll ruminate on this and a potential solution and figure out what to do for the next revision or sub-revision.
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Reference: molly/MacroPad#2
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