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sburrow
PostPosted: Fri Jan 13, 2023 11:00 am 
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floobydust wrote:
Also, keep in mind that triggering the MCP130 with a momentary switch on the output will NOT reset the internal delay, as the device is not designed to be used in such a circuit. The DS1813 is designed to be used with a manual trigger and will reset it's time delay when the momentary switch is closed.


Hahaha! I completely didn't know that, I was misunderstanding it's operation! Yes, I see that in the datasheet now. So as I understand it, the MCP130 helps with power-on reset only. Why the reset button itself works is because the internal schmitt-trigger on the W65C02! Hm, very interesting developments.

plasmo wrote:
Another approach is put a 220 ohm resistor between 5V and MCP130’s VCC terminal and connect reset button to MCP130’s VCC terminal. Reset button will drop MCP130 voltage and trigger the power-on reset pulse. MCP130 is 50 cents vs $3 DS1813, it is worth the extra resistor if you really want a clean reset every time. I don’t bother with that, personally.


And now that I understand it's proper operation, that new configuration makes sense, hm! I think I'll leave it as it is. Currently it works, and a drop-in replacement with a DS1813 would also work. I'm intrigued by the R+C reset style, but honestly I'm happy with what I have. I have learned a lot just now. Thank you both for that clarification!

Chad
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BigDumbDinosaur
PostPosted: Fri Jan 13, 2023 5:45 pm 
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sburrow wrote:
BigDumbDinosaur wrote:
sburrow wrote:
To keep this short: Don't rely on the resistor+capacitor reset circuit during power-up.

10K is too high a value—the circuit will be noise-sensitive. I’d go no higher than 3.3K.

Is that... with the MCP130 / DS1813 supervisor? Or without?

Without.

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sburrow
PostPosted: Sat Jan 14, 2023 2:15 pm 
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BigDumbDinosaur wrote:
Without.


So, I tried that this morning. I replace the 10K pull-up with a 1K pull-up, just like Ben Eater. I then put the 0.1uF cap back in, just like Ben Eater. And then I removed the MCP130 from the circuit, just like Ben Eater.

And it failed on power-up. Reset button still works fine of course. I tried a few times and it was just not working. Oh well! If it's sensitive as to need a 3.3K vs a 1K or a 10K, then I think I'm happy just using the MCP130. I'm keeping the 10K pull-up with the MCP130 just like last time.

Thanks!

Chad
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BigDumbDinosaur
PostPosted: Sun Jan 15, 2023 6:25 am 
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sburrow wrote:
So, I tried that this morning. I replace the 10K pull-up with a 1K pull-up, just like Ben Eater. I then put the 0.1uF cap back in, just like Ben Eater. And then I removed the MCP130 from the circuit, just like Ben Eater...And it failed on power-up.

No surprise there.

The time-constant of the 0.1µF cap and 1K resistor is only 100µs, much too short for a power-on situation. My experience with can oscillators is most take several 10s of milliseconds to stabilize following power on. Roll-your-own oscillators using a crystal and associated components probably take as long, or longer than a can oscillator. WDC states in the data sheet that reset must stay low for a minimum of two full Ø2 cycles, which means the oscillator must be stable before reset is released. I dunno about the 65C02, but I can tell you that the 65C816 will not come out of reset if that two-cycle minimum is not satisfied.

Devices such as the MCP130 and DS1813 typically hold reset down for 150-250 milliseconds to assure VCC stabilizes and other circuit elements, mainly clock generation, are up-and-running before the MPU is allowed to start. Arranging the Ben Eater reset circuit so it will produce a 250 millisecond delay on power-up, but with using a more reasonable 3.3K resistor, would require a timing capacitor of approximately 70µF. That assumes the MPU sees the low-to-high transition of reset as valid around 3 volts. Resistance in series with the reset push button would be de rigueur to limit the capacitor discharge current to a safe level when manually resetting the machine.

That said, the trouble with doing reset Ben Eater-style is it will not cleanly reset any device whose input isn't Schmitt-triggered. And, of course, an inverter is needed to handled devices that use an Intel-style reset, e.g., the 28L92 DUART is such a device when operated in x86 mode. So you’re back to using some silicon in the reset circuit.

Incidentally, the Microchip MCP100 series has a totem-pole output, so no pullup resistor is needed on the reset line. The MPC100’s quiescent current draw is in the microamp range. Therefore, connecting the MCP100 to VCC through a 100 ohm resistor and connecting the VCC pin on the MCP100 to a grounded push button is a practical arrangement. The resulting circuit will give both manual and “automatic” resets without exposing the push button to significant current (50mA worst-case with the button continuously held down).

Attachment:
File comment: Microchip MCP100-Series Reset Controller
reset_controller_mcp100-315d.pdf [292.79 KiB]
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sburrow
PostPosted: Mon Jan 16, 2023 8:27 pm 
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BigDumbDinosaur wrote:
No surprise there.


Oh! Haha, I had tried that because you made it sound possible!

BigDumbDinosaur wrote:
The time-constant of the 0.1µF cap and 1K resistor is only 100µs, much too short for a power-on situation. My experience with can oscillators is most take several 10s of milliseconds to stabilize following power on. Roll-your-own oscillators using a crystal and associated components probably take as long, or longer than a can oscillator. WDC states in the data sheet that reset must stay low for a minimum of two full Ø2 cycles, which means the oscillator must be stable before reset is released. I dunno about the 65C02, but I can tell you that the 65C816 will not come out of reset if that two-cycle minimum is not satisfied.


100us = 100,000ns, yes? OH, but you are saying during power-on it would take longer than that just to get power all over the board, etc. Ah ok.

BigDumbDinosaur wrote:
Arranging the Ben Eater reset circuit so it will produce a 250 millisecond delay on power-up, but with using a more reasonable 3.3K resistor, would require a timing capacitor of approximately 70µF. That assumes the MPU sees the low-to-high transition of reset as valid around 3 volts. Resistance in series with the reset push button would be de rigueur to limit the capacitor discharge current to a safe level when manually resetting the machine.


Oh that's a MUCH bigger capacitor. I'm ok without all of that.

Well, good info here, I'm learning. And I've learned that the MCP130xxxD is perfectly fine for my needs. It's a 'drop in replacement' for the DS1813 (with my particular board's setup) yet cheaper. Thank you BDD, I appreciate learning from you.

Chad
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GARTHWILSON
PostPosted: Mon Jan 16, 2023 8:51 pm 
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sburrow wrote:
100us = 100,000ns, yes? OH, but you are saying during power-on it would take longer than that just to get power all over the board, etc. Ah ok.

It will probably take the power supply longer than that to come up to spec.  But perhaps more than that, it takes the crystal in the crystal oscillator time to get to vibrating.  Its selectivity is extremely sharp, such that any change in a crystal's resonating amplitude, including what it takes to get it resonating, is resisted, as that requires frequencies outside what it wants to vibrate at.  For example, I just looked up the data sheet of a 12MHz can oscillator on Mouser, stock number 520-TCH1200-X, and it says it may take up to 10ms for its output to get going.

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sburrow
PostPosted: Mon Jan 16, 2023 9:36 pm 
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GARTHWILSON wrote:
But perhaps more than that, it takes the crystal in the crystal oscillator time to get to vibrating.  Its selectivity is extremely sharp, such that any change in a crystal's resonating amplitude, including what it takes to get it resonating, is resisted, as that requires frequencies outside what it wants to vibrate at.  For example, I just looked up the data sheet of a 12MHz can oscillator on Mouser, stock number 520-TCH1200-X, and it says it may take up to 10ms for its output to get going.


Wow! Whelp, yet another reason for me to be happy with what I have. It was a fun experiment, and I learned a lot, and most importantly I learned that the Ben Eater way is not always "correct". Possible, but not ideal.

Thank you!

Chad
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BigDumbDinosaur
PostPosted: Mon Jan 16, 2023 9:49 pm 
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sburrow wrote:
BigDumbDinosaur wrote:
No surprise there.

Oh! Haha, I had tried that because you made it sound possible!

Well, it is possible...with the right parts. :D

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BigDumbDinosaur wrote:
The time-constant of the 0.1µF cap and 1K resistor is only 100µs, much too short for a power-on situation....

100us = 100,000ns, yes? OH, but you are saying during power-on it would take longer than that just to get power all over the board, etc. Ah ok.

To echo what Garth noted (and I noted some posts ago), crystal-controlled oscillators do not instantly start oscillating when power is applied. And once they do start, their output “jumps around” a bit before the crystal is vibrating at the right frequency (also, the frequency will drift a tiny bit as the oscillator’s internal temperature rises). Power supplies do not instantly go to full output the moment mains power is applied—the output monotonically rises at a rate that is not entirely predictable.

So you’ve got the combination of the power supply’s turn-on time added to the time required for the oscillator to start and stabilize. That's why devices such as the DS1813 and MCP1xx are voltage-sensitive and hold reset down for several hundred milliseconds.

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BigDumbDinosaur wrote:
Arranging the Ben Eater reset circuit so it will produce a 250 millisecond delay on power-up, but with using a more reasonable 3.3K resistor, would require a timing capacitor of approximately 70µF...

Oh that's a MUCH bigger capacitor. I'm ok without all of that.

Whatever produces a clean reset of the required minimum duration is fine. As long as you understand that the Ben Eater circuit will not produce a clean reset due to lack of contact debouncing, there is no reason to not use it. As is often the case with electronics (and life in general), simple solutions aren't always good solutions.

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agsb
PostPosted: Fri Jan 27, 2023 12:00 am 
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Anyway, an alternative. Comments are full welcome :)


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GARTHWILSON
PostPosted: Fri Jan 27, 2023 1:13 am 
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agsb wrote:
Anyway, an alternative. Comments are full welcome :)

In "4k7 uF," "4k7" is a way to print 4.7K (ie, 4700) on parts where the writing would be very small and the decimal point might be lost, or in part numbers or stock numbers where they don't want dots in them.  4k7uF would be approximately the size of my thumb.  4.7µF and the resistors there would give suitable time constants though.

Next, there's no need for a pull-up resistor on the output of a 74HC part.  74HC pulls up just as hard as down, and will bring the output all the way to 5V if the load is light.

See Fairchild's ap. note on HCMOS crystal oscillators at https://web.archive.org/web/20180311021 ... AN-340.pdf .

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BigDumbDinosaur
PostPosted: Fri Jan 27, 2023 7:09 am 
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agsb wrote:
Anyway, an alternative. Comments are full welcome :)

I can't read your schematic. Can you repost in monochrome?

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barnacle
PostPosted: Fri Jan 27, 2023 8:32 am 
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In the UK and Europe, an informal convention has arisen that uses R, k, M as decimal markers for resistor values; p, n, U as markers for capacitor values, and U, m, H as markers for inductor values.

Thus: 4k7 = 4.7 kOhms; 1p8 = 1.8 pF, 10M = 10 MOhms, 470U = 470 uF, 0R1 = 0.1 Ohms and so on. One difference between UK and US systems is that for a long time US values were given as powers of six - 1000pF - while UK values have for many years been powers of three - 1nF for the same part.

On passive component order codes, you often see capacitance values marked using R as a decimal place - 4R76 might be a 47 uF, 1R8 might 1.8 pF. However, there are at least two standards for marking surface mount resistors; and SM capacitors are *never* marked unless they're tantalum or aluminium electrolytics.

And if you fancy a programming challenge, try something which can unambiguously derive the manufacturer, component type, and parameters from a part number order code. Trust me, it's not easy; apart from manufacturers not using a common format for values (except for some reason, for tolerance letters) often they have different codes for value or part size between different lines of their own products...

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GARTHWILSON
PostPosted: Fri Jan 27, 2023 9:06 am 
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barnacle wrote:
One difference between UK and US systems is that for a long time US values were given as powers of six - 1000pF - while UK values have for many years been powers of three - 1nF for the same part.

The only power of a thousand that has tended to get skipped in the US is nF; so we commonly have for example .01µF rather than 10nF.  (We still use ns, nm, and probably other nanos though.)  Otherwise we have all the others— exa-, peta-, tera-, giga-, mega- (or meg in the case of ohms), kilo-, [units], milli-, micro-, nano-, pico, femto-, and atto-.  There are more, but even the two on each end of this list are rarely needed.

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agsb
PostPosted: Fri Jan 27, 2023 1:52 pm 
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BigDumbDinosaur wrote:
agsb wrote:
Anyway, an alternative. Comments are full welcome :)

I can't read your schematic. Can you repost in monochrome?


Sorry, that is monochrome :) thanks your patience,


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kernelthread
PostPosted: Fri Jan 27, 2023 4:29 pm 
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That circuit looks like it only generates a reset when you push the button, not when you power the system up. Is that your intention?
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