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After All That, the Reset Still Seems Iffy

November 4, 2015

The reset and millisecond clock interrupt is now on the protoboard but it doesn’t seem quite right.

The reset button works well with the AVR providing a clean 200ms negative pulse on /INT and delaying a few ms after releasing reset before starting the clock.
15-11-04 goodreset

Power on, on the other hand is awful. Below is what happens when i plug in the usb cable. There are several reset sequences and just a bunch of crap. Maybe it’s to do with USB power but i’ve never noticed anything like this before. The resets are up to two seconds apart which would be long enough for the processor to bollix up something.
15-11-04 badreset

I guess maybe I’ll live with it for now and see if i get smarter. I’ve tried out the serial and so on and it seems fine.

UPDATE: It’s not power. I put a probe on VCC and plugged it in. The power spikes a bit but only within the first dozen or so milliseconds. Maybe its the RTS line? Yup, RTS is all over the place for several seconds. I don’t know what to make of that. I may just live without auto-reset for a while but i’ll check the connections first.
15-11-04 badreset RTS

I sampled the RTS line on an arduino clone that hooks up to the FTDI connector and saw exactly tthe same kind of mess. I tried applying power by turning on the PC and got a smooth transition. Powering on by plugging in the USB cable is just not a good idea with RTS-reset active.

ALSO: The whole idea of using the avr as a reset seems questionable at least the way i’ve done it. For one thing, while the AVR is held in reset (say I hold the button down) the Z80’s reset line is floating so it’s running free!

From → Olduino/Z

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