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

For the life of me, I can't remember. I remember seeing it in one of Recom's application notes, either for overvoltage or reverse voltage protection.

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

Of course switching regulators like this weren't available back in the day, but it's well known that linear regulators require a protection diode in certain circumstances, the goal being to prevent current from flowing backwards through the regulator at powerdown.

Although superficially that may seem impossible, it can occur in certain circumstances. For example, the circuit (the load) attached to the regulator output may include considerable capacitance due to the bypass caps that are present, and that capacitance will contain stored energy. At powerdown, that energy needs to be discharged, and if the regulator input voltage plummets too rapidly, current will pass backwards through the regulator (unless the protection diode is present).

A look at the Recom datasheet (attached) reveals that their handy little switching regulator likewise faces that powerdown issue, and a protection diode may be required for that reason. (The datasheet also suggests a minimum load of 10 mA, which presumably explains GamerFox's inclusion of R2 and R3.)The datasheet doesn't mention zener (or other) diodes shunted to ground, so I'm drawing a blank on that subject. If such a precaution were necessary you'd think the datasheet would mention it. But possibly the App Note GamerFox mentioned explains it. (I'm also drawing a blank on zener diodes being used as shunts for linear regulators back in the day. Maybe Garth can clarify.)


Um... bus ack lines? Not sure what you could mean by that. The Motorola 68000 bus protocol involves a Data Transfer Acknowledge signal, but there's nothing similar in the 65xx context. If you wanna overclock a 65xx you can just keep cranking up phi2 as far as you like. At some point your system will go off into the weeds, and that's how you know you've gone too far!

-- 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

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http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

Thanks, Garth. Switching reg's have gotten quite a lot smaller but evidently they did and still do need a zener shunt sometimes.

I spent some time looking around at http://www.recom-power.com but I was unable to locate the App Note GamerFox mentioned. But presumably the App Note is where the zener part numbers in the schematic (BZX79C5V6-T50A and BZX79C3V6) came from, isn't that right, Gamerfox ?

-- Jeff

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

_________________
http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

Originally it was MMSZ4690T1G and MMSZ4685T1G but they were SMD-only

e: it's in this sheet https://recom-power.com/pdf/Innoline/R-78C-1.0.pdf

I took BDD's advice and changed the memory mapping a little. Here's the decoder circuit sheet.

_________________
http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

Mixing and matching the HC and LS types might not be ideal either.

But yeah, that amount of gates, there’d be a solid 50-60nS delay going on there.

The actual logic also looks incorrect. The "BANKZERO" signal, labelled with no bar, is actually active low. Any access to bank 0 would result in all four output selects (nEXTRAMSEL, nROMSEL, nIOSEL, nLORAMSEL) all going high, i.e. inactive.
This sort of thing is a good application for a PLD of some sort. If you could make do with 7 IO chip selects instead of 8 and 4 bank address bits (1MB address space), you could fit it all onto a 22V10. Even better, if you used a 1502/7032 you could fit the bank select latch on there as well.

If I were to go use a 22v10 it looks like I'd have to change the primary power rail to 5V leading to needing level shifters for the SD card and display.

You can use the low voltage version, the ATF22LV10C-10PU. It's rated for use down to 3.0 volts and has a 10ns rating. I was going to suggest this, but you already did yourself

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

Not sure about the display, but there are many microSD card modules that run from 5v and have the level shifters built in (and provide a handy 0.1" pin header thing)

I'm using them on my Ruby boards which are all 5v.

-Gordon

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--
Gordon Henderson.
See my Ruby 6502 and 65816 SBC projects here: https://projects.drogon.net/ruby/