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I own several AT89C4051 microcontrollers and I'm currently trying to read signature bytes of the micros that I probably broke (by applying 7.2V to the VCC pin before noticing the 5V regulator became a short circuit between input and output) and I want to read signature bytes of the good micro.

Currently I use an RC setup (1uF pull-up electrolytic capacitor + 10K pull-down carbon-film resistor) on the XTAL1 pin and short the capacitor as attempt to increment the clock by one pulse but I feel this isn't the best approach because the voltage at XTAL1 would slowly fall in voltage and that might confuse the micro.

I read how schmitt triggers and flip-flops might rectify this, but I'm looking for something simple without alot of part count. I mean I could go with a 74HC14 but I'll be wasting 5 out of 6 gates in the package.

Whats the simplest way using the fewest parts to create a clean clock signal without relying on an ultra slow oscillator? I want to increment manually with a button.

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  • \$\begingroup\$ You might be wasting several gates but you would only be using one component. What could be more efficient? You could parallel the other gates to drive an LED to show the status of the clock. \$\endgroup\$ – Transistor Oct 31 '18 at 18:58
  • \$\begingroup\$ Mike, is a 555 okay? Because they work really good as a way to convert a bouncing manual PB into a nice, clean single clock pulse event. A 74121 would have been another possible suggestion, some time ago. But I think they are getting harder to find these days. There are many options, so I think you need to say a little more about what you are excluding and why. Also, with a 556 and an external crystal clock source, you could have a switchable source (either PB or XTAL) and feed the MCU from that. You can then operate single-step or XTAL (or between single-step and variable 555 timer, too.) \$\endgroup\$ – jonk Oct 31 '18 at 19:55
  • \$\begingroup\$ Also look at Ganssle's part 1 and Ganssle's part 2 for some thoughts about debouncing your PB. I've also got a few 2-transistor circuits that would work. There are lots of ways to go. \$\endgroup\$ – jonk Oct 31 '18 at 20:51

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