Thanks both Stephen and Brian for working on QUAD and Brian for the dive
into the history and sharing some of the gotchas discovered.
I think this last version looks very nice
* we have power all the time, using the VDD or RAMRST signal as power
source
* Due the diodes, we get to use the RAMRST as power source, but also
allow to backfeed
* the flip-flops retain their state, as they are powered by the same
VMEM, so everything
should be preserved on reset/power-cycle
* There is even a free diode on Pin 4 of the BAV04 one could connect a
local CR2032 backup battery
(... if it can be made fit on the board)
I like it.
I have a 128kx8 (LP621024) in my project drawer, I think I'll start
building one of these to get some experience in seeing how I can use
bank-switching when writing software for the M100.
(different footprint, so I'll have to spin a new board; will send a pull
request),
Thanks,
Henner.
On Tue, 23 Aug 2022 at 13:39, Brian K. White <[email protected]> wrote:
> Updated. The main branch is now essentially v006 which adds back in a
> diode I'd removed which backfeeds ramrst when vcc has power (to keep the
> internal ram disabled), plus switched U2 to power from vmem, so now all
> logic and ram are powered from vmem together, and same as before removes
> the resistor-cap power-on-reset.
> https://raw.githubusercontent.com/bkw777/reQUAD/main/PCB/reQUAD.svg
>
> What was main below is now branch v008.
> --
> bkw
>
> On 8/23/22 04:10, Brian K. White wrote:
> > Steve raised a couple questions about my changes to QUAD that I don't
> > have good answers for, so I added all my previous versions into that
> > github repo as branches named v001, v002 etc, because at least a few
> > of those DO work, especially the early versions before I got all hack
> > happy.
> >
> > v002 is the version that exactly matches the QUADv2 schematic on
> > bitchin100
> > https://github.com/bkw777/reQUAD/tree/v002
> >
> > I think I must have gotten my versions 1 & 2 files mixed up.
> >
> > Looking at the different schematics, it looks like the progression goes:
> >
> > v002 -initial - identical schematic to QUADv4 original (new pcb layout
> > though)
> > https://raw.githubusercontent.com/bkw777/reQUAD/v002/PCB/reQUAD.svg
> > For comparison:
> > http://bitchin100.com/wiki/images/7/7b/QUAD_schemactic.png
> >
> > v001 - add schmidt triggers to power-on-reset output (I think this is
> > an idea Steve might have suggested to me to try)
> > https://raw.githubusercontent.com/bkw777/reQUAD/v001/PCB/reQUAD.svg
> >
> > v003 - add a diode across the p-o-r resistor (I might have got this
> > from reading about r/c p-o-r circuits in general)
> > https://raw.githubusercontent.com/bkw777/reQUAD/v003/PCB/reQUAD.svg
> >
> > v004 - junk
> > https://raw.githubusercontent.com/bkw777/reQUAD/v004/PCB/reQUAD.svg
> >
> > v005 - remove p-o-r, switch to a non-resettable flipflop, power
> > flipflop from vmem (fail to power u2 from vmem)
> > https://raw.githubusercontent.com/bkw777/reQUAD/v005/PCB/reQUAD.svg
> >
> > v006 - same schematic as v005, pcb layout changes only (pull the chips
> > in from the ends so that a chip-puller doesn't hurt anything)
> > https://raw.githubusercontent.com/bkw777/reQUAD/v006/PCB/reQUAD.svg
> >
> > v007 - junk (but one correct change: move U2 to vmem)
> > https://raw.githubusercontent.com/bkw777/reQUAD/v007/PCB/reQUAD.svg
> >
> > main - junk - move ramrst, unshuffle the address lines output from U4
> > so that Q0 -> A0 Q1->A1 etc no idea if that was ok, I intended to test
> > https://raw.githubusercontent.com/bkw777/reQUAD/main/PCB/reQUAD.svg
> >
> > So I think what we want is v006 but change U2 to get power from vmem.
> > Or one of v001,2,3 I'm not sure which is best, but any of 1-3 is
> > probably safe and more or less the same as the original.
> >
> >
> > At least a few of those versions do work, or at least appear to. I did
> > build a few and run them, but my testing was only cursory.
> >
> > I think until further notice, consider this stuff food for discussion
> > only, not claimed to be good, especially the last version.
> >
>
>
> --
> bkw
>
>
