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I wish to create a new DMA/RAM expansion card for the Tandy 1000 line.

Great Hierophant

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As long as it's combinatorial only 'L' variant. If its an 'R' or 'V' registered variant (containing flip-flops), it becomes more difficult. If the security bits are not set, you could just read the fuse data out with a programmer.

Tandy appears to have only used 82S153s when they needed programmable logic in the 1000 and its initial add-on boards. They are simple combinatorial logic chips that can be easily replaced.
 

Eudimorphodon

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If you are interested, I can post the schematics online as a starting point for you. Or with enough poking, I could pick both designs up again and push forward.

I would have released a PLUS memory expansion a long time ago (I have 6-8 other PLUS cards designed but not produced) if I could find a suitable solution to the high-stacking shrouded 62 pin IDC connectors. But, the ultimate board would be a two card stack with it's own mating system that would provide an upward facing PLUS connector for a 3rd card of choice. I was thinking IDE (or SD card), RAM, RTC, MPU-401, 1x serial, and NE2000.

Having just become the proud owner of a memory-expansion-less 1000 EX count me as someone who would be thrilled if you (or anyone) were to pick up this ball and run with it! I've just started looking for possible solutions to this issue and I've seen a number of mentions of the possibility of making a direct port of the JR-IDE board (combo memory+IDE) that could fit the Tandy systems. If you ever feel like laying that out I'd love to take a crack at getting a PCB from a board mill and populating it, if necessary.

A serial port and RTC would be an excellent bonus, of course.
 

dJOS

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Having just become the proud owner of a memory-expansion-less 1000 EX count me as someone who would be thrilled if you (or anyone) were to pick up this ball and run with it! I've just started looking for possible solutions to this issue and I've seen a number of mentions of the possibility of making a direct port of the JR-IDE board (combo memory+IDE) that could fit the Tandy systems. If you ever feel like laying that out I'd love to take a crack at getting a PCB from a board mill and populating it, if necessary.

A serial port and RTC would be an excellent bonus, of course.

There is another option:

https://www.tindie.com/products/CyberneticSys/tandy-1000-ex-hx-plus-isa-riser-card/

+

https://texelec.com/product/lo-tech-1mb-ram/

+

any half height dual serial card

+

https://www.tindie.com/products/CyberneticSys/tandy-1000-ex-smartwatch/ (I'm out of DS1216's atm tho)

:cool:
 

Eudimorphodon

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I did see that, and I guess that would work for chose-any-two-of RAM, IDE, or serial, and totally don't get the idea I'm discounting your product...

But, well, it would still be great to have a single card for it at least two of those, like the JR-IDE does for the PCjr. Or... crazy idea: have you considered the idea of making a version of your riser that has a RAM expansion? When looking through eBay for Plus memory cards (ha!) I ran across this bizarre thing someone built. (And total respect to you if you're a member of this forum, it's awesome.) Here's a link to the auction:

https://www.ebay.com/itm/Duo-Slot-512K-RAM-Card-for-the-Tandy-1000-1000A-Last-one-/273735338008

The card consists of a 512k SRAM chip on a riser with two slots for adding the same cards we might want in an EX/HX to the "wasted" space in an original Tandy 1000. Obviously the clearances are tighter in an EX (I don't have the machine near me to tear into it and measure), but... what if there was *just* enough space to fit an SRAM on there along with the slots?
 

dJOS

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No dramas, my stuff is made as part of my hobby so I dont mind if folks want other solutions. :cool:

I did reach out to the maker of that board and asked if I could use his schematic but he never replied unfortunately. :(

That said I am working on a Riser card design using Jame's (of lo-tech fame) 1 MB board as the base design ... however it's overkill for our needs and I'm working on simplifying it .... I cant provide any guidance as to when it'll be ready unfortunately (just started a new more senior role and time poor atm).
 

blackepyon

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Yeah, most of us are just fellow hobbyists who just want to see this stuff made. Problem is that not everybody has the time (day jobs, family, whatnot). Still want to get that made eventually.

As for that memory board, I've heard that lo-tech 1MB card apparently works in the Tandy 1000 EX/HX just fine with dJOS's PLUS riser, so that should at least get you by until one of us can get some PLUS boards going. I don't know if the EX/HX support Upper memory blocks or not, and the motherboard has 256K built in, so you need about 384K of that 1MB.
 

Eudimorphodon

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I did reach out to the maker of that board and asked if I could use his schematic but he never replied unfortunately. :(

Aw, foo. I was actually going to open a thread specifically about that thing and ask if anyone had the schematic for it to see if I could just possibly try cooking up something like that myself. Or, at least, just the additional RAM part. I'm planning to put a modded Gotek in my machine so I'm not sure I'm *that* bothered about having the IDE interface, in the near term. But I've been coming to the conclusion that I'm probably going to need more than 256k to experience at least a plurality of Tandy-specific video games.

Maybe at some point I'll noodle over the lo-tech schematics and see if I can work it out. It certainly looks like you don't need a lot of glue to just hang an SRAM off of an ISA-ish bus and it shouldn't be too hard to lay that out. Famous last words.
 

Eudimorphodon

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I don't know if the EX/HX support Upper memory blocks or not

Really stupid idea: According to the EX technical manual the blocks at D0000 and E0000 are open, and it looks like that's where the IBM PCjr mapped its cartridge slots. I wonder if you could map 128k in there, load it with the contents of a PCjr cartridge, and fire it off.

Granted that's mostly a theoretical question given the amount of PCjr cartridge software that actually exists...
 

blackepyon

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Really stupid idea: According to the EX technical manual the blocks at D0000 and E0000 are open, and it looks like that's where the IBM PCjr mapped its cartridge slots. I wonder if you could map 128k in there, load it with the contents of a PCjr cartridge, and fire it off.

Granted that's mostly a theoretical question given the amount of PCjr cartridge software that actually exists...

I don't see why not, since those cartridges are basically just ROMs in a slot, and the EX/HX can boot from ROMs. I was referring more to RAM and applications that specifically were written to take advantage of UMB, or how the existing blocks on the Tandy 1000 where the UMB section would be that are dedicated to ROM and video, are addressed or reshuffled if that area is used as RAM. That's one of the things I was hoping to test with my prototype, but I've since gotten sidetracked.
 

blackepyon

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Aw, foo. I was actually going to open a thread specifically about that thing and ask if anyone had the schematic for it to see if I could just possibly try cooking up something like that myself. Or, at least, just the additional RAM part. I'm planning to put a modded Gotek in my machine so I'm not sure I'm *that* bothered about having the IDE interface, in the near term. But I've been coming to the conclusion that I'm probably going to need more than 256k to experience at least a plurality of Tandy-specific video games.

Maybe at some point I'll noodle over the lo-tech schematics and see if I can work it out. It certainly looks like you don't need a lot of glue to just hang an SRAM off of an ISA-ish bus and it shouldn't be too hard to lay that out. Famous last words.

I think the early Sierra games could run with 256K, but yeah, it's really limiting without that RAM expansion.

Mainly, you need to figure out the addressing logic on that 688 for whatever memory section you need. That's what the jumper pins on the 1MB card set.
 

blackepyon

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I meant the 1000A not the HX/EX.

You see them floating around now and then, but they're not too common. I've got a generic one with 512K that I was reverse engineering for the DMA controller (Tandy specific interface) that I was hoping to sell once I was finished with it. Good news though, is that because that machine actually has 8-bit ISA slots, Lo-Tech's 1MB RAM card is just the quick fix you need if you can get by without DMA, so that's what most people do.
 

Eudimorphodon

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I don't see why not, since those cartridges are basically just ROMs in a slot, and the EX/HX can boot from ROMs. I was referring more to RAM and applications that specifically were written to take advantage of UMB, or how the existing blocks on the Tandy 1000 where the UMB section would be that are dedicated to ROM and video, are addressed or reshuffled if that area is used as RAM. That's one of the things I was hoping to test with my prototype, but I've since gotten sidetracked.

Yeah. Mostly what I was thinking there is if that 128k block in the Tandy EX/HX was really free as the tech manual seems to imply that might be a good place to map the extra 128k you'll have left over from a 512kx8 SRAM after you backfill up to 640k. (32 pin 512kx8s seem to be readily available in DIP form, so that's promising; I can kind of handle through-hole but been too much of a wimp to tackle surface mount yet.) If there's software that works on XTs that will let you take advantage of statically mapped UMBs then you should be able to use it there? The PCjr cartridge thing was just a random idea for a stupid pet trick you might be able to pull off with RAM mapped there.

Most of my DOS knowledge is at least 20 years stale, I have a lot of catching up to do. Even if there's something as simple as a RAMDISK driver that would let you use a 128k UMB on an XT that could be useful for that old trick of copying command.com to it.
 

blackepyon

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Yeah. Mostly what I was thinking there is if that 128k block in the Tandy EX/HX was really free as the tech manual seems to imply that might be a good place to map the extra 128k you'll have left over from a 512kx8 SRAM after you backfill up to 640k. (32 pin 512kx8s seem to be readily available in DIP form, so that's promising; I can kind of handle through-hole but been too much of a wimp to tackle surface mount yet.) If there's software that works on XTs that will let you take advantage of statically mapped UMBs then you should be able to use it there? The PCjr cartridge thing was just a random idea for a stupid pet trick you might be able to pull off with RAM mapped there.

Most of my DOS knowledge is at least 20 years stale, I have a lot of catching up to do. Even if there's something as simple as a RAMDISK driver that would let you use a 128k UMB on an XT that could be useful for that old trick of copying command.com to it.

What I don't know about UMB is whether the system detects and manages that extra RAM, or if the software has to specifically look for it or already be configured with the addresses.
 

Eudimorphodon

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What I don't know about UMB is whether the system detects and manages that extra RAM, or if the software has to specifically look for it or already be configured with the addresses.

So far as I'm aware no PC knows anything about UMBs? From what I recall you generally configure them either in hardware using an EMS 4.0-capable memory card or with the appropriate MMU-tickling software on 386 and later machines.

This look like a super useful thread:

http://www.vcfed.org/forum/showthread.php?31753-Loading-dos-high-on-a-XT

Therein is a memory card design that looks like might be a predecessor to the lo-tech card using a 512k SRAM chip and showing the decode circuitry, and referencing drivers like USE!UMBS.SYS and DOSMAX.

UMBs aside, the Tandy manual seems to show the A0000 block is also free. I wonder if it would be kosher to map another 64k there contiguously with the rest of it and just throw out the 64k at B0000 for 704k. (Apparently the Tandy machines mirror the memory buffer used by video in low memory to the normal CGA location so mapping the whole 512k contiguously would be out.)

I'm starting to think at this point I need to order the SRAM chip and get a piece of protoboard so I can have them on the shelf mocking me. No, gotta hack FlashFloppy onto that GoTek first...
 

rkrenicki

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I'm also working on an all-in-one PLUS CompactFlash storage card based on the XT-IDE/CF-IDE for the Tandy 1000 EX/HX.

I know I am pretty late to the party here, but I actually just finished designing one of these. It is basically a modification of the XT-CF-Lite V4.1 to use the PLUS bus instead. I just sent the design off for fabrication of some prototype boards earlier today.

I also sent you a PM about another matter.
 

blackepyon

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I know I am pretty late to the party here, but I actually just finished designing one of these. It is basically a modification of the XT-CF-Lite V4.1 to use the PLUS bus instead. I just sent the design off for fabrication of some prototype boards earlier today.

Sweet! The more, the merrier. Too few cards were made for this bus, despite how popular the EX/HX were. Do you have a good source for mounting brackets? My idea was to use a cutout of PCB soldered on at a right angle to keep costs down.

As per usual, everything draws attention away from my "hobby," but I'll have to redo my own design anyways since Altium's cloud-based Circuitmaker isn't designed for exporting to other formats (I've tried unsuccessfully to extract from the local files into something readable), which makes it harder to share with anybody not using the service.

I'm using Ki-Cad from now on. CircuitMaker is a really nice program (especially the auto-routing feature, which saves a lot of time in preliminary layout), but being cloud based is proving to be more trouble than it's worth for me.
 
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