On 5/4/2022 10:50 AM, Uffe Jakobsen wrote: > > Jim Brain writes: >> >> On 5/4/2022 10:15 AM, Michal Pleban wrote: >>> Uffe Jakobsen wrote on 04.05.2022 17:01: >>> >>>> How about extending /RESET until your device is ready ? >>> >>> I read that on some C64 boards /RESET is quite a strong output? >>> >>> >> On the 296 boards, it's the output of a 555 timer, and is extremely >> hard to overcome. >> > > Isn't the output of the the reset "timer-circuit" driven by 7406 and a > pull-up on all board revisions ? > > Regards Uffe > Nope: https://www.lemon64.com/forum/viewtopic.php?t=46277&start=0 Response (bottom third of the page) from skoe: " We found out that ASSY 326298 REV A actually has an unusual reset circuit. It is not implemented like it is shown in the schematic #326106. Instead of using an open collector output and a pull-up resistor, they left out the pull-up R36 and connected the reset line directly to the push-pull output of the NE556. This is surely an obvious design flaw. They fixed it in the next revision. Bad news: The NE556 can drive +/- 200 mA (!!!) according to its datasheet. This is too much to be overridden by the EasyFlash logic. I think only a mechanical reset button can do this (or very strong logic outputs)." Max machine has the same issue: http://www.zimmers.net/anonftp/pub/cbm/schematics/computers/c64/maxschematic.jpg Jim -- Jim Brain brain_at_jbrain.com www.jbrain.comReceived on 2022-05-04 19:00:58
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