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Topic: Tutorial - How to change firmware on 8u2 (Read 116 times) previous topic - next topic


ant.b - this worked great. I have a few things to figure out, but with a little modification, my uno thinks and looks like a joystick. Thank you so much for posting your tut! :)

Brad Needham

Clarification for reply #10.  According to the datasheet, the chip looks at the HWB pin state as reset is released (on the rising edge of /Reset).  So you should take the wire off the reset pin before taking the wire off the HWB pin.  If you take both wires off at once, it's a matter of luck whether the HWB pin is still grounded when you release the reset pin.

So to save frustration, I recommend following the datasheet, and remove the Reset wire before you remove the HWB wire.


There's a certain amount of capacitance in the Uno circuit though (you are touching the wire against a capacitor, charging it). That's why, if you take off both wires together, it should still be low at the reset. On my board it holds enough charge to stay low for at least half a second.

Brad Needham

Ah, that's a nice feature: being able to yank both wires at once and the cap takes care of enforcing the HWB state requirement.  Thanks for that detail.

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