Myarc 512K card modification

[+9640News]

Is there anyone that has the time and skill to modify the Myarc 512K card to be used as memory for the Geneve 9640? Preferably someone that has done this before AND has the time?

 

The big question is someone that has the free time to do so with the electronics skill. I've looked my 512K card over, and I question my ability to skillfully do the work.

 

Beery

 

[fabrice montupet]

Yes, looking at the long documentation Paolo Bagnaresi wrote in 1989, the modification takes some time and needs some skill and patience but, sure gets some fun
Hope, you'll find someone that will accept to modify your great card. Even several years of searches, I have never found one to upgrade my Geneve 9640.
For my part, for this time I am very busy and I have already many works to finalized. But, I would be happy to help you later if you've not found someone to do the job.

[peterfleeman]

Well, I wouldn’t want to make any promises, but i have Marc Hull’s already modified card as an example. And I have an unmodified card to experiment on. I will study the instructions and see if anything in there scares me off. I don’t claim to have tons of skill or experience, but I have some. And I’m loaded with patience. The trouble with me is time. I’m traveling for work until Friday. Then it’s just a couple weeks until traveling again for the holidays. So it might be a month before I get the job done. But if you’re ok with all that, I’m happy to try!

[+9640News]

Hey Peter, no disrespect, but the "I'm happy to try!" statement is something that made me a bit nervous. I could just as well "try" myself. Was hoping to find someone that has already done the mods and know the "gotchas" if there were any.

 

I would not want you to risk an attempt with your one and only Geneve.

 

If anyone had a modified 512K card and wanted to trade it for an unmodified card, I would be receptive to that opportunity as well.

 

Beery

[+Ksarul]

I have a couple of the boards that I plan to modify myself, Beery--but that probably won't take place until the Christmas break. . .we can talk about getting yours done after that if you like, as then I'll have some recent experience doing the mod.

[+FarmerPotato]

Is there anyone that has the time and skill to modify the Myarc 512K card to be used as memory for the Geneve 9640? Preferably someone that has done this before AND has the time?

 

The big question is someone that has the free time to do so with the electronics skill. I've looked my 512K card over, and I question my ability to skillfully do the work.

 

Another angle: is there a schematic for a Geneve only 512K expansion?

It could be safer to make a card from scratch than modify a 4A card.

[peterfleeman]

Fair enough! I would still like to look into the process. I had not even heard it was possible until recently. Can anyone post a link to a copy of the instructions?

[fabrice montupet]

I don't remember where I've found the document, so here is a link to my hosting space : www.ti99.com/misc/Myarc512K-MODIF.pdf

Edited November 26, 2018 by fabrice montupet

[fabrice montupet]

Another angle: is there a schematic for a Geneve only 512K expansion?

It could be safer to make a card from scratch than modify a 4A card.

That's a great idea!

[+9640News]

I have a couple of the boards that I plan to modify myself, Beery--but that probably won't take place until the Christmas break. . .we can talk about getting yours done after that if you like, as then I'll have some recent experience doing the mod.

 

I'm not in any rush, so that sounds feasible. There were several other messages others posted after your posting. If someone wants to design a 512K board, I think that would be great for several Geneve users. Not sure if there is even anyone up to the task though.

Beery

[peterfleeman]

I don't remember where I've found the document, so here is a link to my hosting space : www.ti99.com/misc/Myarc512K-MODIF.pdf

 

Thanks Fabrice! I read through most of the instructions, and I am confident I can handle it. The instructions are very thorough! I think I will go ahead and attempt it with the extra card that I have. If all goes well, I would happily trade it for your unmodified card, Beery. This way, between Ksarul or myself, you should be all set in a month or so.

[+9640News]

Sounds good Peter.

Beery

[+arcadeshopper]

 

I'm not in any rush, so that sounds feasible. There were several other messages others posted after your posting. If someone wants to design a 512K board, I think that would be great for several Geneve users. Not sure if there is even anyone up to the task though.

Beery

 

I'd buy one

[Shift838]

 

I'm not in any rush, so that sounds feasible. There were several other messages others posted after your posting. If someone wants to design a 512K board, I think that would be great for several Geneve users. Not sure if there is even anyone up to the task though.

Beery

 

I'd buy one too!

[+InsaneMultitasker]

This update is not for the faint of heart. Troubleshooting any problems will require strong will and patience to work through them. Myarc had trouble converting these cards and we ran into the same challenges at Cecure due to component issues, among other things. I worked through the entire process once, maybe twice, and declined any further updates from that point forward. To me, the modification was not worth the time and effort though the extra memory can be beneficial so if you are up to the challenge, go for it.

 

One thing that concerns me is whether this version of the modification takes into account the external bus/peripheral cards. For example, page 0xBA corresponds to the peripheral cards at visible space 0x4000-0x5FFF. Someone will want to validate that this version does not present any risk of conflict between active peripheral cards and active memory pages on the 512K card.

 

I would think a new 512K card would be relatively simple to glue together with a single SRAM and interface logic. Get away from all the DRAM and its pitfalls now that low cost SRAM is available and keep the component count to a minimum.

Edited November 27, 2018 by InsaneMultitasker

[+9640News]

Tim,

 

Blocking page >BA from the Geneve's general memory map is pretty easy. If I am not mistaken, at one point in time, that memory page was excluded from the list in MDOS. Even if it is not, I had code I released I think in 9640News, if not elsewhere, that one could run from the Autoexec file and block that memory page.

Beery

[RickyDean]

I did a couple of the old style modifications on two or three of my Myarc 512 cards, in the 9o's, once you get one finished, the others go pretty quickly.

[+FarmerPotato]

This update is not for the faint of heart. Troubleshooting any problems will require strong will and patience to work through them. Myarc had trouble converting these cards and we ran into the same challenges at Cecure due to component issues, among other things. I worked through the entire process once, maybe twice, and declined any further updates from that point forward. To me, the modification was not worth the time and effort though the extra memory can be beneficial so if you are up to the challenge, go for it.

 

One thing that concerns me is whether this version of the modification takes into account the external bus/peripheral cards. For example, page 0xBA corresponds to the peripheral cards at visible space 0x4000-0x5FFF. Someone will want to validate that this version does not present any risk of conflict between active peripheral cards and active memory pages on the 512K card.

 

I would think a new 512K card would be relatively simple to glue together with a single SRAM and interface logic. Get away from all the DRAM and its pitfalls now that low cost SRAM is available and keep the component count to a minimum.

 

New build ocurred to me because I'm currently debugging 512K SAMS in a sidecar (it's killing reads from the module space when A9 is high).

 

The vintage TMS4500 DRAM controller is on eBay for $5-$9, not to say DRAM itself.

 

I checked Mouser last night..

A 512K x 8 SRAM in 3.3V is $4 for SOJ-36 1.27mm pitch. 71V424S12YG

Add 4 of TI's LVC245A (they can do the job of a 244 too, and bridge 5V to 3.3V),

a small PAL to block the reserved address pages,

voltage regulator for 3,3V,

caps

and bingo.

 

None of the chips would be socketed,

 

Could probably even get PCB with assembly included for $50.

Edited November 27, 2018 by FarmerPotato

[+InsaneMultitasker]

Blocking page >BA from the Geneve's general memory map is pretty easy. If I am not mistaken, at one point in time, that memory page was excluded from the list in MDOS. Even if it is not, I had code I released I think in 9640News, if not elsewhere, that one could run from the Autoexec file and block that memory page.

The fix you refer to has been in place since before I started maintaining the OS. It will stop the OS from using the page but is only a software solution -- it is best to ensure the card cannot/does not respond to the memory space from a hardware perspective as well. This may include one or more pages in the peripheral bus space 0x88-0x8f

 

I did a couple of the old style modifications on two or three of my Myarc 512 cards, in the 9o's, once you get one finished, the others go pretty quickly.

Agreed, it can go pretty quick after a few unless you run into component or board -related issues.

[+FarmerPotato]

The fix you refer to has been in place since before I started maintaining the OS. It will stop the OS from using the page but is only a software solution -- it is best to ensure the card cannot/does not respond to the memory space from a hardware perspective as well. This may include one or more pages in the peripheral bus space 0x88-0x8f

 

What are all the memory holes that a 512k card should leave unmapped?

 

1. with AMA,AMB,AMC high, >4000 (page >BA)

2. with AMA,AMB,AMC high, >8000 - 9fff for memory mapped peripherals like sound, speech? (page BC)

3. dip switch option to open holes at any AMA,AMB,AMC in case of any nonconforming card in PBOX

Design Notes

pages 80 - C0 are external 512K in pBOX

AMC is most significant address line

>BA must be a hole. This is >4000 in the top 64K.

AMA,AMB,AMC are pulled high in the PBOX.

DIP switch option to open the hole at >4000 for all values of AMA,AMB,AMC

dsr = !a0 & a1 & !a2

mmap = a0 & !a1 & !a2

high = ama & amb & amc

hole = (high | dip) & (dsr | mmap)

https://www.mouser.com/datasheet/2/464/IDT_71V424_DST_20141030-881857.pdf

CS* = memen* | hole

OE* = memen* | dbin = dbin

WE* = memen* | we* = we*

http://www.ti.com/lit/ds/symlink/sn74lvc245a.pdf

lcv245a to data bus:

A side = SRAM

B side = PBOX

dir = memen* | dbin (high: A to B. low: B to A)

oe* = memen* | hole

lvc245a will output high level voltage 3.3V on data pins. This should be greater than VIH of the LS245 of the Geneve. Should be OK.

all other input signals buffered one way through lvc245a

Edited November 27, 2018 by FarmerPotato

[+9640News]

Pages >80 to >BF I believe are the only ones that can be mapped to an external PEBox card for the Geneve without further Geneve card modifications. Pages >BA and >BC are the only two pages that should not be used by the Geneve operating system.

 

If I am not mistaken, a GenMOD Geneve brings the extra decoding for AMD and AME lines. I guess one could theoretically have a GenMOD Geneve and no Memex, and if they had a 1.5 MB or 2.0 MB card, then you would want to map out >3A, >3C, >7A, >7C. I think the final 64K ram at pages >F8 to >FF would also need to be mapped out. Page >F0 and >F1 are tied to the Geneve eprom, so those two would be mapped out. I do not recall details of >F2 to >F7 if those were mapped out on the GenMod/Memex setup.

 

There are so few GenMod Geneve's out there, that I suspect anyone with one has a Memex already.

 

Last, if you were to consider some kind of card to accommodate a GenMOD'ed Geneve, Ron Walters had some chips with < 20 ns response times in some of the circuitry as speed was critical with zero wait states. Myself, I think if someone just built something for a 512K expansion system, that would be sufficient. You could always design for more with no chips being installed so you had only one board layout.

 

Beery

[+InsaneMultitasker]

 

What are all the memory holes that a 512k card should leave unmapped?

 

1. with AMA,AMB,AMC high, >4000 (page >BA)

2. with AMA,AMB,AMC high, >8000 - 9fff for memory mapped peripherals like sound, speech? (page BC)

3. dip switch option to open holes at any AMA,AMB,AMC in case of any nonconforming card in PBOX

I believe the external bus is addressable via pages B8-BF, though I've only tested BA, BB,and BC. Examples of non-DSR (BA) page access include the speech, MBP II card, SID Blaster card. The Genmod documentation has some information about page blocking. A new card that blocks BA and BC would probably meet most needs, unless there is something we have 'forgotten'.

[+9640News]

Yeah, I am about 99% certain >BA and >BC are accessible on the bus. I thought the Rave Speech card answered on page >BC along with the A/D card setup (on prototype board???). Other non fully decoded RS232/Disk controllers would answer on >7A, >BA, and >FA though I think the >F8 to >FF (maybe all of >F0 to >FF) was on the Geneve board itself.

 

Beery

[+9640News]

I have not heard anything from anyone recently. Inquiring if anyone had a working Myarc 512K card modified for the Geneve they would want to trade for an unmodified card?

 

Or, was anyone considering a 512K card for the Geneve?

 

Beery

[RickyDean]

Beery, I have done the modification to Myarc 512k cards, back in the 90's. Three of them and they worked fine, but it, of course has been a long time. I am still plenty capable of doing the soldering, but just haven't had a lot of time this past year. But I can't test a card right now as I do not have a working PEB, that I can trust, or at this moment, a working Geneve to check it with. That will change in a couple of months as I get some time and money to complete my work. So if someone else can do it and get something to you soonest, that would probably be better. But in the process of saying all this, yes I can modify them.