In theory, instead of connecting MCP130's VCC directly to 5V, a 100 ohm resistor can be inserted between power VCC and MCP130's VCC and connect the manual reset switch between MCP130's VCC and ground, so the manual switch simulates a power outage. In practice, I've never done that but instead connecting the manual reset switch between MCP130's reset output and ground. This is because many of my retro designs (such as CRC65) have an alternative bootstrap sequence active in the short time window between reset negating and normal boot sequence execution so I need to know exactly when manual reset is negating in order to invoke the alternative bootstrap sequence. In the course of testings I've discovered the common, inexpensive tactile switch has mostly bounce-free switching so a manual reset switch at MCP130's reset output works just fine vast majority of the time.
Bill

Sorry Ed, but I'll have to disagree with you on this one. What you're suggesting is a flawed design path I don't agree with, e.g..

1- If it works most of the time, then it's fine... nobody should need anything better
2- Giving mediocre advice is acceptable
3- Doing things properly (called engineering) in your view is over-engineering... and not necessary

When someone new shows up, especially with limited or possibly no actual experience, encouragement is great thing. Giving them proper hardware design advice is another.

Based on your comment, every Commodore home machine was over-engineered, as all had a decent reset circuit. Personally, I found most Commodore machines to be on the skimpy side of proper engineering, mostly for cost reasons.

Doing things in a half-*** way can work under a limited set of conditions, but when it doesn't or is intermittent, a new user will tend to get more frustrated and might even give up, especially if the collective advice given here promotes poor design, engineering or build techniques.
A new user could also get confused and think that the software is the problem, which could also lead to a waste of time and more frustration.

Including proper design/engineering into your hobby does NOT make it industrial grade, not even close!

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The missing ingredient here, I think, is context. I'm all for engineering, in its place, but we have topics here and they set a context. A kid on a home made sledge going down a steep hill may or may not get to the bottom in full control. A bobsleigh team on an Olympic course need a different level of discipline.

Robust engineering suggestions can be very welcome, but in their place. And they should only ever suggestions, based on personal experience and preference. There are no stone tablets here.

Why is that?

As a hobbyist coming from zero electronics knowledge roughly two years ago, one of the things that's still elusive to me is picking *specific* resistor values.

What I think is, having a lower value pullup resistor will make RSB go high more quickly (i.e., return to normal after being pulled low for a reset). Is the inverse of that also the case, that using a higher value resistor will make it pull down to GND more quickly, getting a cleaner and more immediate reset signal?

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"The key is not to let the hardware sense any fear." - Radical Brad

For starters, be aware that many use cases for resistors have surprisingly forgiving tolerances -- like, 50% or even more (even though resistors are typically sold with a tolerance of 5% or better).

And pullups are a use case where the exact value isn't terribly fussy. But hobbyists often will, by default, stick with a value such as 2.2k or 3.3k that's familiar because they've seen it used in commercial products or mentioned in a data sheet or application note.

Yes having a lower value pullup resistor will make RSB go high more quickly. As the node goes high and low, you're charging and discharging the parasitic capacitance, and the delay is proportional to R times C.

But the speed with which the node goes low (ie, discharges the capacitance) is mainly determined by the "resistance" of whatever causes the node to go low (in this case, a transistor that's internal to the DS1813). I've simplified matters slightly, but I hope the gist is clear.

-- Jeff

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It is. Thank you!

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"The key is not to let the hardware sense any fear." - Radical Brad

BigDumbDinosaur continues to be our Thesaurus Rex.

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Empirically, MCP101 appears to be 1/5 price but otherwise the same as DS1813. It works with switch and 100 ohm resistors. I presume MCP130 also works. Try it.

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