Sounds like a plan. However, as you have a breadboard, I would suggest that you divide your project into separate functional blocks and use the breadboard to test them. Functional blocks can be things as simple as the supervisory circuit on power up that provides the proper timing for the Reset signal and the Panic trigger for the NMI signal. Another block would be I/O decode... which you can easily test with some LEDs and a dropping resistor on the output of an I/O or memory select signal. The same goes for qualified read and write signals used by memory devices and non-65xx I/O peripheral devices. Get these functional blocks working so you know how they operate and can feel confident that when used in a complete system they will function as intended.

3.3K... well, not that much of a ground rule, but the general consensus with the newer CMOS processors is to use 3.3K for all pull-ups. Sure, you could spend time calculating slew rates versus signal timings and the capacitive load on each signal (IRQ, NMI, etc.), but it's just easy to go with a 3.3K pull-up and call it done. I've actually run at 10MHz clock speeds with no errors, and I always use IRQ-driven I/O on pretty much all (I/O) devices. BTW - I use LEDs (for indication) which are rated at 1ma active current, so a 3.3K works out perfect as a dropping resistor for these as well.

Lastly... just realize that the number 1 goal is to get something working. Also, once you have a working design, you'll obviously get to a point where you'll ditch it for the next design that has more features/functions and newer and better ideas. It's a journey... not a one-off for all of time.

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Regards, KM
https://github.com/floobydust

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x86?  We ain't got no x86.  We don't NEED no stinking x86!

That is indeed the goal, thank you.

Thank you floobydust and BDD for the 3.3K pull-up resistor explanation. Seems like the way to go for sure. And thank you BDD for clarifying the open-collector part. And also thank you for reminding me about the ghost IQR signal, I remember reading that on Garth's page in particular.

And the functional blocks sounds good too, floobydust. I have seen some folks use silkscreen to show those blocks. I will keep that in mind as I continue.

Thank you both very much for your support.

Chad

Just a quick footnote. 10 mA may be reasonable for older LEDs, but modern, high-efficiency LEDs require far less (1 or 2 mA maybe).

Less is more, in the sense that it'll be best to keep the DC loading to a minimum (in the scenario where the LED is being driven by a bus line or a gate, I mean). Also, and perhaps surprisingly, there is such a thing as LEDs being too bright (actually unpleasant to view)!

For these reasons I suggest being prepared to use the largest series resistor possible. And if the resistors are in an array (perhaps a SIP array) that's socketed, you can quite easily change the value after your project is already built.

ETA: I don't necessarily advocate LEDs, by the way. In some situations they're worthwhile (and the certainly parts are inexpensive). But if you don't have single-step then they're perhaps not very useful, and if you're doing a PCB you may decide they consume too much space.

-- Jeff

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In 1988 my 65C02 got six new registers and 44 new full-speed instructions!
https://laughtonelectronics.com/Arcana/ ... mmary.html

Good to note, thank you.

I think BDD started talking about LED's because I said I was working with an LCD, like a 16x2 kind. But either way it's good info.

_________________
x86?  We ain't got no x86.  We don't NEED no stinking x86!

Hey guys. I'm curious if there's any reason I shouldn't use a MOSFET as an inverter for the SCC2691 'RESET' line?

TIA... Mike

Mike, that is a great question. I would also like to know! Thank you all.

Chad

Haven't you forgotten to include a pullup resistor, Michael? (Edit: oops, I see one is indicated) But the idea is workable. Does the incoming signal ( /RES ) swing from 0 to 5 Volts? You'll wanna be sure to select a MOSFET that will turn on sufficiently, given the available incoming voltage.

If your motivation for doing all this is to save space, you might want to consider simply using a 74LVC2G04 instead. This is a miniature SMT device with only 6 pins (and hence only 2 inverters). For more on the 1G and 2G series, see my post, Tiny, superfast gates rival programmable logic.

-- Jeff

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In 1988 my 65C02 got six new registers and 44 new full-speed instructions!
https://laughtonelectronics.com/Arcana/ ... mmary.html

I would watch out for the edge rates: certainly coming out of reset, and possibly going into reset, you need quite a decisive signal. Too slow, and the device might malfunction. (This is a general point: it's possible the specific device here is very defensively designed. Check the spec for the reset input.)

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x86?  We ain't got no x86.  We don't NEED no stinking x86!

And, just by my looking around a bit, the SCC2691 is hard to find, at least in DIP package.

Anyways, new question:

Does the 6522 VIA R/W input need to be qualified with Phi2? I know we have discussed that for RAM (and ROM), but does the VIA also need that same qualification? Would it hurt to use that same line for RAM, ROM, and VIA?

Chad

I remember that post on those fascinating products, Jeff. Thank you.

Actually, that TL770B supervisor chip that Kevin (floobydust) uses isn't very expensive. I just happen to have a bin full of 2N7000's.

I believe 6500 and 6800 peripherals qualify the R/W input with the PHI2 clock input internally.

So... a direct connection. Ok! Thank you.