Yeah, there are a number of ways to deal with the non-standard RAM modules in an M100; the pin spacing of the modules is .75 instead of the standard .60, so you will probably have to make a little adapter board in any case.
A self-contained module has to combine the four discrete chip selects into one, and also re-encode them into the binary upper two addresses. There are various ways of doing that and I have some of the commercial circuits somewhere but can't find them at the moment. One way would be a priority encoder as Fugu suggests. His 32K idea is clever and you could just used diodes to combine the chip selects; as a matter of fact you can also use an 8K chip and use diodes for the encoding instead of the encoder IC. FWIW, the Sony modules use two chips, a 4025 and a 4011. If you don't mind connecting to or modding the main board there are also a number of options, including replacing all 4 RAM chips with one 32K chip; Steve Adolph has a good writeup about that: http://www.club100.org/memfiles/index.php?&direction=0&order=&directory=Steve%20Adolph/mods_to_upgrade_ram m ----- Original Message ----- From: Fugu ME100 To: [email protected] Sent: Wednesday, March 14, 2018 5:14 PM Subject: Re: [M100] 8K RAM Chip If you did not want to use the Libero method you could use a 74HC148 (or similar) 8 to 3 line priority decoder and put the 4 CSx- lines into the upper or lower 4 inputs of the ‘148. That would recreate 2 address lines and a new CS- for the 8Kx8 SRAM. It could all mount on a proto-board and not require any 'soldering to' the M100 :) I would guess the NEC board uses a similar method but with an HC149 8-to-8 line priority encoder. Alternatively use a 32Kx8 SRAM and waste 3/4 of the space, but it would still need the CSx- lines ANDed to generate the SRAM CS-. Again no soldering on the M100 required. From: M100 <[email protected]> on behalf of Mike Stein <[email protected]> Reply-To: <[email protected]> Date: Wednesday, March 14, 2018 at 12:19 PM To: <[email protected]> Subject: Re: [M100] 8K RAM Chip It needs more than just remapping the signals; the required upper two address lines are not available on the sockets so you either need to add logic to recreate them or modify the main board. m ----- Original Message ----- From: Gregory McGill To: [email protected] Sent: Wednesday, March 14, 2018 1:22 PM Subject: Re: [M100] 8K RAM Chip thanks! It seems like we should be able to use the 8x8 chip from the 102 with some kludging of lines.. they are pretty close.. Greg On Wed, Mar 14, 2018 at 10:08 AM, Brian White <[email protected]> wrote: There are at least a few different "build your own ram upgrade" articles on club100 and other archives of old forum posts, and in magazines too I think but those are hard to search. Here's one that is not one of the old original ones I was thinking of, but looks ok. http://digilander.libero.it/rar2k/TRS80/Memory24k.html I have some NEC modules that work that I assume must have originally been meant for nec 8201a. They are a little pcb with a single ram chip and an additional chip probably a decoder of some sort to consume 4 chip-enable lines. I could take some photos of it and maybe it's circuit could be reverse engineered from that. https://photos.app.goo.gl/ZQle2id7AMWdX2bC3 Another option is QUAD, which is a thing that installs in the bus socket and displaces the internal ram with it's own full 32K, plus 3 more banks of 32K that you can switch between. Although you can't get a quad right now. Steven Adolph is testing his latest revision of the design and it's in between right now. He found problems with the old version and so removed it from oshpark, and th new version is not yet verified. But assuming that comes along sooner or later, that would upgrade you to 32K the same as if you had installed all 4 possible modules inside. -- bkw On Wed, Mar 14, 2018, 11:14 AM Gregory McGill <[email protected]> wrote: ok is there a source for the 100 chips? or a pcb? Greg On Wed, Mar 14, 2018 at 12:02 AM, Fugu ME100 <[email protected]> wrote: Just the 102, it uses a standard pin out. The 100 uses a special RAM module. From: M100 <[email protected]> on behalf of Gregory McGill <[email protected]> Reply-To: <[email protected]> Date: Tuesday, March 13, 2018 at 10:58 PM To: <[email protected]> Subject: Re: [M100] 8K RAM Chip oh wait these are 32x8 :) are these ones on ebay for the 100 or 102? or both? Greg On Fri, Mar 9, 2018 at 7:33 PM, Gregory McGill <[email protected]> wrote: if you have the pinouts I have a bunch of 8x8 srams around for TI99 projects Greg On Fri, Mar 9, 2018 at 6:11 PM, Ken Pettit <[email protected]> wrote: Ahh, I see now the original email stated 102. So yeah, those will work. Ken On 3/9/18 6:09 PM, Fugu ME100 wrote: More if it was R/S :) This is the one https://www.ebay.com/itm/1-TOSHIBA-TC5565PL-15-64K-8Kx8-SRAM-CMOS-STATIC-RA M-5V-150NS-28-PIN-PDIP/321974484773?hash=item4af72cbf25:g:ldEAAOSwGotWlWd9 you mean? On 9/3/18, 6:07 PM, "M100 on behalf of Peter Vollan" <[email protected] on behalf of [email protected]> wrote: Wow, a quick check reveals a 8kX8 SRAM on ebay for $3. Didn't those "memory modules" cost about $30? On 9 March 2018 at 17:57, Chris Kmiec <[email protected]> wrote: Great, I'll go looking on the intrawebs :) You don't happen to have another REX, do you? :) Chris On Fri, Mar 9, 2018 at 7:01 PM, Fugu ME100 <[email protected]> wrote: The chips are available they are standard 8Kx8 SRAM. Should be able to find some on line. Unfortunately the QUAD is only for the Model 100, it will not fit the 102. Congratulations on your new addition :) From: M100 <[email protected]> on behalf of Chris Kmiec <[email protected]> Reply-To: <[email protected]> Date: Friday, March 9, 2018 at 4:33 PM To: <[email protected]> Subject: [M100] 8K RAM Chip Are these available anywhere, or do I have to find a donor system? Just got a like-new 102, but no memory expansion. I'm assuming QUAD is no longer being made/sold? Thanks! On Mar 14, 2018 11:14 AM, "Gregory McGill" <[email protected]> wrote: ok is there a source for the 100 chips? or a pcb? Greg On Wed, Mar 14, 2018 at 12:02 AM, Fugu ME100 <[email protected]> wrote: Just the 102, it uses a standard pin out. The 100 uses a special RAM module. From: M100 <[email protected]> on behalf of Gregory McGill <[email protected]> Reply-To: <[email protected]> Date: Tuesday, March 13, 2018 at 10:58 PM To: <[email protected]> Subject: Re: [M100] 8K RAM Chip oh wait these are 32x8 :) are these ones on ebay for the 100 or 102? or both? Greg On Fri, Mar 9, 2018 at 7:33 PM, Gregory McGill <[email protected]> wrote: if you have the pinouts I have a bunch of 8x8 srams around for TI99 projects Greg On Fri, Mar 9, 2018 at 6:11 PM, Ken Pettit <[email protected]> wrote: Ahh, I see now the original email stated 102. So yeah, those will work. Ken On 3/9/18 6:09 PM, Fugu ME100 wrote: More if it was R/S :) This is the one https://www.ebay.com/itm/1-TOSHIBA-TC5565PL-15-64K-8Kx8-SRAM-CMOS-STATIC-RA M-5V-150NS-28-PIN-PDIP/321974484773?hash=item4af72cbf25:g:ldEAAOSwGotWlWd9 you mean? On 9/3/18, 6:07 PM, "M100 on behalf of Peter Vollan" <[email protected] on behalf of [email protected]> wrote: Wow, a quick check reveals a 8kX8 SRAM on ebay for $3. Didn't those "memory modules" cost about $30? On 9 March 2018 at 17:57, Chris Kmiec <[email protected]> wrote: Great, I'll go looking on the intrawebs :) You don't happen to have another REX, do you? :) Chris On Fri, Mar 9, 2018 at 7:01 PM, Fugu ME100 <[email protected]> wrote: The chips are available they are standard 8Kx8 SRAM. Should be able to find some on line. Unfortunately the QUAD is only for the Model 100, it will not fit the 102. Congratulations on your new addition :) From: M100 <[email protected]> on behalf of Chris Kmiec <[email protected]> Reply-To: <[email protected]> Date: Friday, March 9, 2018 at 4:33 PM To: <[email protected]> Subject: [M100] 8K RAM Chip Are these available anywhere, or do I have to find a donor system? Just got a like-new 102, but no memory expansion. I'm assuming QUAD is no longer being made/sold? Thanks!
