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This is a circuit I whipped up for an attempt to make a negative-edge triggered detector with inverted output.

The logic needs to be the following:

If input is high, output is high.

If input goes from low to high, output is high.

If input goes from high to low, output goes low for enough time to process data. I'm specifically trying to turn the WR pin on an 82C55 chip into an edge-triggered pin.

This is my circuit and I believe I arranged the parts correctly, but I do not know how to determine the optimal values of each part, except that for R2, I'm going to use maybe 10K to limit current, and I think C2 needs to be higher than C1 to prevent debouncing from the previous chip.

The input is directly connected to a GPIO line of an AT89C2051 microcontroller.

What can I do to make this circuit work at its best without making the speed too slow or too fast?

circuit

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So basically, you need a differentiator, with the output pulled "high". Did you try a simple RC network?

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ I'm trying to understand whether that would be sufficient because I don't want the state to slowly drain from one level to another and confuse the target chip (which is the WE pin of the 82C55). I'll look into this circuit and see if it can help tho. \$\endgroup\$ – user116345 Nov 26 '16 at 5:51

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