The difference between Home use and Commercial, is simply volume. Commercially, if you have a jig you can do anything :-) It is not like these boards were repairable - Replacement would be much cheaper than repair.
It may not be wise, but it can give you a leap ahead from the opposition. I believe this practice is now common enough that some modern flash devices are often provided in dual pinouts (one reversed) to increase density. Kindest regards, Doug Jackson em: [email protected] ph: 0414 986878 On Thu, 25 Aug 2022 at 05:12, MikeS <[email protected]> wrote: > I've mounted chips 'upside-down' like that myself; never dreamed anyone > did it commercially. > > m > > ----- Original Message ----- > From: "Brian K. White" <[email protected]> > To: <[email protected]> > Sent: Wednesday, August 24, 2022 2:36 AM > Subject: Re: [M100] How to shadow the RAM with own RAM from the system bus > bay ? > > > > Heads up though, Steve has me convinced about that (A)* idea he > > mentioned in an earlier post. > > > > I've made a new version based on that idea but it needs some testing to > > work out how hard (A)* should be pulled, a dead short or a resistor of > > what value? A simple short would make the pcb simpler but right now I > > made room and got an 0805 footprint crammed in there. > > > > I'm going to rig up a test using one of my older version boards that I > > already have without needing to wait for it to be made. My latest > > versions were just like this with the only difference being (A)* is N/C. > > That's convenient because it's trivial, all that needs is a single bodge > > wire from bus pin 16 to gnd, maybe through a resistor. > > > > The idea is, original QUADv4 disables the internal ram by holding RAMRST > > high, which ends up blocking /OE on all the internal ram. > > > > The new idea is leave RAMRST alone (other than using it for power, but > > don't override it), instead, hold (A)* low. This blocks the (A)* signal > > output from M20 reaching M3 & M4 input, which prevents any /CE1-/CE16 > > from being selected. > > > > So rather than having all the internal ram active but just output > > disabled, the ram is all inactive. > > > > It's still overriding something, it just goes from overriding RAMRST to > > overriding (A)*. (A)* is an output from M20, and I don't know what it > > means for M20 to just short an output to gnd, but Steve already said he > > tested it and it seems fine, and other commercial products even > > supposedly did that. > > > > What I want to do is see if maybe a resistor can pull it down good > > enough to inhibit M3 & M4 from activating, and see just what it takes. > > Maybe the output is pretty strong and maybe it takes a pretty low value > > resistor to overcome it, but maybe anything is better than nothing and > > maybe we can at least reduce the current through that output a little. > > Or maybe a simple trace is no problem after all. Either way I want to > > try it to find out. > > > > This version is in the v011 branch until it's tested. > > > > https://raw.githubusercontent.com/bkw777/reQUAD/v011/PCB/reQUAD.svg > > https://github.com/bkw777/reQUAD/tree/v011 > > > > The pcb is done too, and the bom is good except it's missing the > > resistor. But no links to buy a pcb because this isn't verified yet. > > > > > > That's not a bad idea about the on-board battery. The PG Design version > > of this has an on-board battery, but it's a bit more complex device and > > works somewhat differently since it does not conflict with the internal > > ram. The internal ram becomes bank1, and the added ram is banks 2 > > through 8 depending on what size model. It's pretty handy that you can > > remove the device and not lose the contents. > > http://tandy.wiki/PG_Design > > https://photos.app.goo.gl/m8rpRFAL22FcjxLu6 > > > > That device looks a bit more complicated though to allow not fighting > > with the internal ram, and have a battery without draining it > > immediately. For one thing, most of it's logic is actually all in a PAL. > > (the chip with the barcode sticker on it in the pics there) > > > > > > A similar device from Cryptronics also had a battery, a larger 3-cell > > pack connected by wires, soldered, and stuffed in between the optrom & > > bus socket. > > > > https://photos.app.goo.gl/68qSfxdPD9WwdhzHA > > > > Looks like a user bodge, but I've seen other pictures and they > > apparently all shipped this way. I have one but have never fired it up, > > so I don't know if it blocks out the internal ram or not. That thing has > > a lot going on "the hard way" with no PAL. > > > > The silkscreen says 64K, but there *appears* to be 96K worth of chips. > > There are 12 chips, but they are stacked and you can only see the > > markings on the top set, which is 4 x 6264, which is 4 x 8KB for 32K. > > It's possible the hidden chips are not 6264, or possible the unit is a > > revision that stuffs more ram onto the same pcb. > > > > Those chips on the bottom of the pcb are actually installed upside down > > from the point of view of the pcb surface, but it's so they can be in > > same orientation as the rest of the stack. That's why you can't read any > > markings. Notice the injection mold marks. The entire stack of 3 chips > > must all be connected parallel right through the board except for a > > couple control lines. They must have had to bend all those pins with a > jig. > > > > Lot of hand work on that puppy. > > > > -- > > bkw > > > > > > On 8/23/22 22:52, Henner Zeller wrote: > >> 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] > >> <mailto:[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 > >> < > 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 > >> <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 > >> < > https://raw.githubusercontent.com/bkw777/reQUAD/v002/PCB/reQUAD.svg> > >> > For comparison: > >> > http://bitchin100.com/wiki/images/7/7b/QUAD_schemactic.png > >> <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 > >> < > 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 > >> < > https://raw.githubusercontent.com/bkw777/reQUAD/v003/PCB/reQUAD.svg> > >> > > >> > v004 - junk > >> > > >> https://raw.githubusercontent.com/bkw777/reQUAD/v004/PCB/reQUAD.svg > >> < > 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 > >> < > 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 > >> < > 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 > >> < > 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 > >> < > 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 > >> > > > > > > -- > > bkw >
