I have a design with a ATmega32U4 that I'm trying to do DFU with. I have a hardware reset button that's confirmed working, as well as a button for HWB with no pullup attached.
When I erase program memory, it seems like it jumps straight to DFU mode and I'm able to load firmware using FLIP. However, when I do have a program flashed, it doesn't seem to go into DFU mode when I do a reset with power plugged in while holding HWB low. I've confirmed that the HWBE fuse is set on the device.
Looking at this timing diagram, it shows HWB going high after reset before becoming Don't Care, but I'm not sure if that transition is strictly required. Could the issue be the lack of an external pull-up on HWB? I assumed HWB would be pulled up internally, but that may be a bad assumption.
Thanks in advance!