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
On 8/22/22 13:48, Brian K. White wrote:
A few things about ram for the 100...
1 - Just to get it out of the way for completeness, if you just want
to fill out the 32k, then you can build or buy normal 8k modules.
https://github.com/bkw777/Model_T_RAM
2 - Several years ago Steve had a thing called QUAD which does this
ramrst trick. He stopped producing it and took it down from oshpark so
that people didn't unwittingly buy it after he determined that it had
a little problem that it didn't reliably reset to itself to bank 0 on
power-cycle. Plus I think there was some conflict between the 0QUAD
driver software and REXMGR or REX itself which was never resolved.
However, for the purpose of study, you can read about it and look over
the schematic here: http://bitchin100.com/wiki/index.php?title=QUAD
3 - Since then I have taken that QUAD info and made a modified
version, and Steve has graciously granted me permission to share that
derivative work from his. For my part, I think the original reset
problem just doesn't matter much and am willing to accept it since I
think it's recoverable by just resetting again or at worst by issuing
the controlling poke actively, plus, I've never actually seen it
happen. But even beyond that, I also decided to simply remove the
resistor-cap resetter and just power all the logic at all times along
with the ram, so it never needs to reset. I also just accept the
compatibility limitation and just don't use one in the same machine
with a REX. I usually use rex image backups rather than ram banks
anyway and the rex is more useful than extra ram banks all in all. But
I still wanted to explore it just academically for the heck of it even
if I don't use it generally. You can look over that here:
https://github.com/bkw777/reQUAD
I wouldn't order any parts or pcbs immediately. I haven't built and
tested the latest version yet, but I do have the parts and pcbs for a
slightly earlier version that's only different cosmetically, same
circuit, so I'll throw one together and double-check it. It was about
a year ago the last time I played with this, other than just now
putting together the public stuff yesterday, so it's worth a
verification.
Thanks again Steve.
--
bkw
