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

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  • Eudimorphodon
    replied
    Originally posted by blackepyon View Post
    LOL! Everybody seems to wire up that '245 wrong the first time.
    (I'm not blameless there either )
    Yeah, guilty as charged here.

    I wonder if I should offer my flawed boards as some sort of door prize, since they only take a single wire to fix.

    Leave a comment:


  • blackepyon
    replied
    Originally posted by dJOS View Post
    Adrian has posted an update here:

    LOL! Everybody seems to wire up that '245 wrong the first time.
    (I'm not blameless there either )

    Leave a comment:


  • blackepyon
    replied
    Originally posted by Eudimorphodon View Post
    Dang it, that's a good idea, and it would give me an excuse to put different silkscreen doodles on every card. Maybe for the next round.

    The gerbers passed the pre-manufacturing sniff test so they're on the way to the presses now. I'm both excited and thrilled with dread that something isn't going to be right. The usual.



    That's the main reason why I'm not sure it's worth adding the DMA controller, because an 8-bit Soundblaster is one of a *very* short list of things I can think of that would even use DMA on an XT class machine... and most of those things that could use it really kind of need a faster machine anyway. I mean, it'd be useful if you needed to run an old school XT disk controller, but if you have XTIDE built in instead then that reason *and* the improved floppy performance justification both kind of go out the window. (Although I guess the latter might break a few demos, possibly?)

    A far out thing that occurred to me is I think those old hand scanners that used 8-bit ISA cards needed DMA. I had one back in the day and I have to admit I'd find it amusing to play with one again. But I also remember it not running that well on the 286-12 I had it connected to, so just like any software that needs a Soundblaster I suspect it'd be a tough row to hoe for the Tandy to make any use of it.
    I've been thinking about that as well. DMA 0 is out of the question, since as has already been established, the newer SRAM doesn't need that refresh pulse, and the onboard RAM is being refreshed by Big Blue anyways. So really, it's just those "insane builds" with the riser expansions that could really take advantage for that rare card that actually needs it. I wouldn't mind trying my SoundBLASTER 2.0 Pro in 8-bit mode just to see if it can run it.

    Another thing one needs to consider for these "insane builds" is the limited number of IRQs the 1000 EX/HX have available. As I see it, only IRQ 2,3,4 are available on the expansion header, since everything "needed" is already built onto the motherboard. At least one of those is going to be taken by the serial card for your mouse, then if you add a NIC and sound card, IF they support those IRQs, you're pretty much full unless you want to run the risk of conflicts. The parallel port on my I/O card seems to work without an assigned IRQ (at least in send mode for the blinkenlights circuit I cobbled together), though I'm not sure serial would if you're using it to run a mouse.

    Leave a comment:


  • rkrenicki
    replied
    I had seen the video, I was wondering if he had some more stress testing that might have been outside of the scope of the video.

    Leave a comment:


  • dJOS
    replied
    Originally posted by rkrenicki View Post
    @misterblack How happy have you been with the 00/32 addressing logic setup that you have? Have you run into any issues with it? It would be quite a bit smaller than the addressing logic that I have been working with..
    Adrian has posted an update here:

    Leave a comment:


  • rkrenicki
    replied
    @misterblack How happy have you been with the 00/32 addressing logic setup that you have? Have you run into any issues with it? It would be quite a bit smaller than the addressing logic that I have been working with..

    Leave a comment:


  • Eudimorphodon
    replied
    It looks like my new PCBs are in the mail, so if everything goes okay I might be soldering one together by next weekend. A few people have expressed interest in getting a set of boards, if the design works I'll have plenty of extras...

    One thing I wanted to throw out there, re: the discussion of what type of IDE plug to use. For this round of boards I went with a right-angle 44 pin female 2mm pitch, because that seemed like a really convenient choice that would allow direct-plugging of inexpensive IDE-to-CF and IDE-to-SD connectors. (And for the record, I still think it's a good idea.) I do want to publicly gripe, however, about the fact that apparently right-angle 2mm female plugs are harder to source than I anticipated. (When I'd initially googled them it looked like no problem, but the devil was in the details.) Digikey has a couple different designs in stock but they cost about $4.50 and $6.50 each respectively, and the $6.50 one is the more correct choice. *Male* right-angle 2mm box headers are no problem, easily found for about a buck each. I ended up buying a couple each of the male and female plugs; they do have direct-plug "DOM-style" 44-pin CF adapters with female plugs on them, and there's always the option of using a cable, so I'll build one each way. (I might have to flip sides of the board for a male plug(?), but I don't think clearance will be a problem) Maybe $6 for the female plug isn't that big of a deal since it still allows using the cheaper adapters, but, bleah.

    It looks like what those aforementioned DOM-style CF adapters do is just edge-mount a straight female connector (which are also cheap), if this goes another rev that could be a strategy to try. It looks a little fragile to me but it's probably fine.

    Leave a comment:


  • Eudimorphodon
    replied
    Originally posted by bladamson View Post
    PS: @Eudimorphodon - You should make a whole line of expansion cards, and name each of them after a different dinosaur.
    Dang it, that's a good idea, and it would give me an excuse to put different silkscreen doodles on every card. Maybe for the next round.

    The gerbers passed the pre-manufacturing sniff test so they're on the way to the presses now. I'm both excited and thrilled with dread that something isn't going to be right. The usual.

    PS PS: As far as soundblasters, I think any game that will run on these machines will probably only support ad-lib anyway, and those are much simpler and require no DMA. Add a couple of OPL3s to the card *instead* of a DMA controller! Haha.
    That's the main reason why I'm not sure it's worth adding the DMA controller, because an 8-bit Soundblaster is one of a *very* short list of things I can think of that would even use DMA on an XT class machine... and most of those things that could use it really kind of need a faster machine anyway. I mean, it'd be useful if you needed to run an old school XT disk controller, but if you have XTIDE built in instead then that reason *and* the improved floppy performance justification both kind of go out the window. (Although I guess the latter might break a few demos, possibly?)

    A far out thing that occurred to me is I think those old hand scanners that used 8-bit ISA cards needed DMA. I had one back in the day and I have to admit I'd find it amusing to play with one again. But I also remember it not running that well on the 286-12 I had it connected to, so just like any software that needs a Soundblaster I suspect it'd be a tough row to hoe for the Tandy to make any use of it.

    Leave a comment:


  • bladamson
    replied
    I have one of those Tandy 1000/1000A RAM/DMA cards. I don't remember the specifics off the top of my head, but IIRC it just has a couple of simple PALs on it. Nothing that could have flipflops or anything, just straight-though logic. So it ought to be pretty easy to build a truth table from it. I can loan the card to one of you, if you want to try to dump the chips, but I want it back when you're done. :P

    In other news, I paid myself today and bought most of the parts for my project. Now the anxious wait begins, since I am a cheapskate and always choose the slowest shipping.

    PS: @Eudimorphodon - You should make a whole line of expansion cards, and name each of them after a different dinosaur.

    PS PS: As far as soundblasters, I think any game that will run on these machines will probably only support ad-lib anyway, and those are much simpler and require no DMA. Add a couple of OPL3s to the card *instead* of a DMA controller! Haha.
    Last edited by bladamson; November 1, 2019, 05:29 PM.

    Leave a comment:


  • Eudimorphodon
    replied
    Originally posted by rkrenicki View Post
    Unfortunately, the original Tandy 1000/1000A memory board, while it did use an 8237.. It used a GAL for some of the address logic, and it has not been dumped.
    I don't imagine that would be too much of a barrier, although if the GAL also controlled any buffering it might be sort of annoying to replicate it. (There's a GAL like that on the motherboard that controls the '245 that's in front of all the motherboard peripherals, both memory and port-mapped. But the equations for that are in the manual.)

    I'd probably have tried harder to find time to curl up with the tech manual, Sergey's schematics, and the Essential PC Hardware Book to sort it all out, but I pretty firmly convinced myself that DMA wasn't a thing that bothered me before then. I think I still have a Soundblaster AWE32 in the garage but I don't think a DMA chip would help me much with that... and the card's a foot long anyway.

    Leave a comment:


  • rkrenicki
    replied
    Originally posted by Eudimorphodon View Post
    Having the schematics from one of the really old Tandy 1000 RAM boards that used a discrete 8237 would make life a little easier but it didn't look like adapting the generic design would be impossible.
    Unfortunately, the original Tandy 1000/1000A memory board, while it did use an 8237.. It used a GAL for some of the address logic, and it has not been dumped.
    That said, the T512CLK memory expansion by ATD was a standard ISA card with the 8237 DMA controller and no programmable logic to be seen.. but they are VERY uncommon.

    Leave a comment:


  • Eudimorphodon
    replied
    Originally posted by blackepyon View Post
    Yeah, I'm happy to see that this thread has taken off, despite my not having as much time as I'd like to work on it.
    If you get more time the other day I was squinting at one of Sergey M's older XT replication projects and it got me thinking again about the OP of this thread, IE, making a board that does include the DMA function. I still don't think it's really necessary for anything I'd want to do so I don't think I'm going to do it, but when I was experimenting with seeing how much room is left on a 100x150mm-ish board after dragging what's on my current RAM board onto it, well... it kind of looked to me like the DMA controller circuitry from this might be fit-able in that much space. Having the schematics from one of the really old Tandy 1000 RAM boards that used a discrete 8237 would make life a little easier but it didn't look like adapting the generic design would be impossible.

    Today was a slow day so I scribbled out a quick design for an ISA riser for my network card and just submitted all three boards; decided I needed to **** or get off the pot because I think I was starting to fall into a "the best is the enemy of the good" cycle of thinking about all the better ways I could rearrange things. Fingers crossed I didn't make any boneheaded mistakes.

    One other aside; I happened to discover that it's apparently still possible to buy Realtek 8019AS chips new for about $3 each. It looks like it basically only takes a serial EEPROM and a set of magnetics to make an ethernet card out of one, so... that's another idea, I guess. (A really goofy thought that occurred to me while reading the manual for the chip is it has built-in ROM/Flash decoding; it's intended for a boot room, but if you made a combo card with XTIDE you could technically use that to hold the XTIDE bios...) I need to quit whining and get on the fine pitch SMT soldering train for that project, though.

    Leave a comment:


  • rkrenicki
    replied
    I finished my initial layout of my 3-in-1 expansion board, but I am waiting for my memory design test boards to arrive before I send it off for manufacturing. I need to do some layout optimization, but I do have it on a 135x98mm PCB right now with some breathing room. I was toying with the idea of going 4-layer, which should let me shrink that down even more by not having to worry about power routing.

    I do have a CF port directly on the board sticking out the rear of the computer, much like my XT-CF-Lite that I already have in the machine.. that said.. Does anyone know of any open source SD-to-CF or SD-to-IDE designs that I could try to incorporate to use SD cards instead?

    Leave a comment:


  • blackepyon
    replied
    Originally posted by misterblack View Post
    I'd be worried about using this type of connector: if they stop making those adapters suddenly it would be much harder to use your board. Versus 40 pin IDE which would be used with a ribbon cable to whatever is available or these types of plug in adapters which take power right from the PIN 20. I used using these nice and cheap SD card slot mount IDE to SD adapters from China (in regular PCs) but they just suddenly stopped making them.

    [ATTACH=CONFIG]56954[/ATTACH]

    Just my $0.02
    That particular CF adapter is my favourite. But yes, they are dime a dozen. For myself, I'd ad a 2-pin header onto the board just for the +5v should it ever be needed. It doesn't take up much space, and you don't need to populate it if you don't need it.

    Leave a comment:


  • blackepyon
    replied
    Originally posted by misterblack View Post
    Suddenly we had no real options and suddenly we have a bunch!
    Yeah, I'm happy to see that this thread has taken off, despite my not having as much time as I'd like to work on it.

    Leave a comment:

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