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

  1. #481
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    The "key" with ordering from Digi-Key is to keep a shopping cart open for your various projects, and wait until it totals over $100, that way you save by getting free shipping. Unless I need something right away, this is how I order. And when you order cheap components, like 74xx ICs, resistors (10k especially), diodes, etc, order more than you need, so you have spares for trying new ideas on a breadboard and prototyping future designs.

    If someone has just one card other than the RAM card it's probably either the useless modem card or the somewhat less-useless serial card.
    I've got the Tandy DMA/RAM card, my "PLUS" ISA-CF, and an ISA multi-I/O card on a PLUS to ISA ribbon that has to be folded upside down to make the entire stack fit.
    My vintage systems: Tandy 1000 HX, Tandy 1100FD, Tandy 1000 RSX, and some random Pentium in a Hewitt Rand chassis...

    Some people keep a classic car in their garage. Some people keep vintage computers. The latter hobby is cheaper, usually takes less space, and is less likely to lead to a fatal accident.

  2. #482
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    Quote Originally Posted by blackepyon View Post
    I've got the Tandy DMA/RAM card, my "PLUS" ISA-CF, and an ISA multi-I/O card on a PLUS to ISA ribbon that has to be folded upside down to make the entire stack fit.
    I guess the way I phrased the sentence was open to interpretation, what I meant was "what Plus card are you likely to find inside of a 256k EX/HX, if it has a card, that you might actually want to keep using?". My EX came with the modem, and I did happen to see an HX with just the serial card on eBay at one point.

    (The modem card in particular doesn't seem to be "rare", I kind of wonder if the 256K machine + modem combo was at some point positioned as a cheap terminal for getting into Compuserve or whatever.)
    My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs

  3. #483
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    Besides the RAM card, the RS-232 card would be the most useful, since you could connect an external modem to it, or a mouse.
    My vintage systems: Tandy 1000 HX, Tandy 1100FD, Tandy 1000 RSX, and some random Pentium in a Hewitt Rand chassis...

    Some people keep a classic car in their garage. Some people keep vintage computers. The latter hobby is cheaper, usually takes less space, and is less likely to lead to a fatal accident.

  4. #484

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    Quote Originally Posted by blackepyon View Post
    Besides the RAM card, the RS-232 card would be the most useful, since you could connect an external modem to it, or a mouse.
    I run a mouse plus a WiModem 232 from my serial card and I know a lot of other EX / HX owners would like to do the same.
    My Retro Collection:
    CBM: C64, Amiga 500 x2, 600 & 1200
    Apple's: IIc, Mac SE, LCII, LC630 & Power Mac G3/233 Desktop
    PC's: K6-III+ 500 System + Roland MT-32 & Tandy 1000 EX 640kb, 3.5" FDD, CF-IDE 4GB HDD
    Visit my Tindie store for Tandy 1000 Adapters for EX, HX, SX, SL, TX & TL etc

  5. #485
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    Quote Originally Posted by dJOS View Post
    I run a mouse plus a WiModem 232 from my serial card and I know a lot of other EX / HX owners would like to do the same.
    I forgot about that. Personally, I'd prefer a hardwired NIC, but the wireless serial "modem" would definitely be useful. You could combine a NIC with a dual RS232 onto one card, maybe with a breakout cable if space is short (right-angle 10-pin .100" header for the second COM port maybe? We've all got those rear-panel-mount serial thingies lying around). Quick check looks like it's possible to fit two DB-9's and an RJ-45 between the screw holes, but you'd need an extension/adapter for the wireless modem.

    I'm thinking you could have a DB-9, an RJ-45, a second RS232 on a 10-pin .100" breakout header for a DB-9/DB-25, and a USB port for 5v external power (or integrate an 8-bit USB controller if you're feeling REALLY ambitious). It would be a really tight squeeze, but it should all fit in the back panel slot.
    My vintage systems: Tandy 1000 HX, Tandy 1100FD, Tandy 1000 RSX, and some random Pentium in a Hewitt Rand chassis...

    Some people keep a classic car in their garage. Some people keep vintage computers. The latter hobby is cheaper, usually takes less space, and is less likely to lead to a fatal accident.

  6. #486

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    Quote Originally Posted by blackepyon View Post
    The "key" with ordering from Digi-Key is to keep a shopping cart open for your various projects, and wait until it totals over $100, that way you save by getting free shipping. Unless I need something right away, this is how I order. And when you order cheap components, like 74xx ICs, resistors (10k especially), diodes, etc, order more than you need, so you have spares for trying new ideas on a breadboard and prototyping future designs.
    This, for sure. You've got to take advantage of the bulk pricing break points. If you spend ~$300 now to stock up on all the basic logic gates, discretes (10k resistor packs and pullups, and bypass and filter caps in particular), breakaway headers, etc, you'll save a pile of money in the long run. They really nickle and dime you to death on small quantities. You pay about 10 cents more per IC buying quantities <10. Resistors are even worse.

    Jameco sells some nice component kits.
    -- Lee

    May Be Interested In Acquiring: Mac IIsi, Quadra 840AV, Commodore PC(286+)/64C/128D, PC-era Tandy stuff, Peculiar Old Serial Terminals.
    Old Computer Fun! (Muh Projects Blahg) | Muh YouTube Channel that goes with it

  7. #487

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    So I've spent part of the morning trying to figure out the most efficient way to handle the bus driver(s)' /enable decoding for my multifunction card. My first thought was to use a single '245 and a little glue logic to combine all the /reads and /cardselects to drive the '245, since the RAMs, IDE latches, drive, and 8255 have their own CS signals anyway, so they'll be tri-stated off the B-side of the data bus when they're not being accessed. ... I *think*. Lol.

    This would be easier if I didn't have to deal with memory and IO devices on the same card. The glue logic to sort that out with a single '245 quickly becomes larger than just using more than one '245. So I guess I'll use at least two, one hooked to /ior and one to /memr, handling memory and io devices completely separately. I *think* I can probably use the same '245 for both IDE and the 8255. The 8255 circuit is really simple, and it *looks* like none of that mess of transparent latches nor the drive itself on the IDE side of things will be contaminating the B-side of the data bus while /ide-cs is un-asserted. But I am not 100% confident of that last statement...

    I do have a regular XT-IDE card. Maybe I need to just breadboard out a little test circuit to tell me if anything gets driven on the B-side while /ide-cs is unasserted and clip it on there and see for sure.....

    It may also be possible that the memory doesn't *need* a '245. The Lo-Tech ram implementation uses one, but the Option-ROM section of the XT-IDE does not. And I think Adrian had the same ram chips working well in his circuit without a buffer, once he sorted out the chinajunk. However, my gut feeling is to keep the buffer, and also to redesign the ROM section a little to make use of it.

    How are you guys handling the bus drivers on your multifunction cards?
    -- Lee

    May Be Interested In Acquiring: Mac IIsi, Quadra 840AV, Commodore PC(286+)/64C/128D, PC-era Tandy stuff, Peculiar Old Serial Terminals.
    Old Computer Fun! (Muh Projects Blahg) | Muh YouTube Channel that goes with it

  8. #488
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    Quote Originally Posted by bladamson View Post
    So I've spent part of the morning trying to figure out the most efficient way to handle the bus driver(s)' /enable decoding for my multifunction card. My first thought was to use a single '245 and a little glue logic to combine all the /reads and /cardselects to drive the '245, since the RAMs, IDE latches, drive, and 8255 have their own CS signals anyway, so they'll be tri-stated off the B-side of the data bus when they're not being accessed. ... I *think*. Lol.

    This would be easier if I didn't have to deal with memory and IO devices on the same card. The glue logic to sort that out with a single '245 quickly becomes larger than just using more than one '245. So I guess I'll use at least two, one hooked to /ior and one to /memr, handling memory and io devices completely separately. I *think* I can probably use the same '245 for both IDE and the 8255. The 8255 circuit is really simple, and it *looks* like none of that mess of transparent latches nor the drive itself on the IDE side of things will be contaminating the B-side of the data bus while /ide-cs is un-asserted. But I am not 100% confident of that last statement...

    I do have a regular XT-IDE card. Maybe I need to just breadboard out a little test circuit to tell me if anything gets driven on the B-side while /ide-cs is unasserted and clip it on there and see for sure.....

    It may also be possible that the memory doesn't *need* a '245. The Lo-Tech ram implementation uses one, but the Option-ROM section of the XT-IDE does not. And I think Adrian had the same ram chips working well in his circuit without a buffer, once he sorted out the chinajunk. However, my gut feeling is to keep the buffer, and also to redesign the ROM section a little to make use of it.

    How are you guys handling the bus drivers on your multifunction cards?
    You could probably do one '245 for each, IOR and MEMR. What are you using the 8255 for?
    My vintage systems: Tandy 1000 HX, Tandy 1100FD, Tandy 1000 RSX, and some random Pentium in a Hewitt Rand chassis...

    Some people keep a classic car in their garage. Some people keep vintage computers. The latter hobby is cheaper, usually takes less space, and is less likely to lead to a fatal accident.

  9. #489
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    I just finished soldering and initially smoke testing my new I/O board that has the IDE port and the DUART behind the same buffer and, knock on wood, doesn't seem to be a problem. (I've run the Checkit diagnostic on both serial ports and hard disk, both passed. But I haven't exercised it more than that.) I just combined the respective chip selects with a spare AND gate.

    Likewise my memory board has the RAM and Flash chips sharing a '245, again just combining the chip selects with an AND. So as long as you're fine with two '245s, one each for mem and i/o, a 7408 or similar should do the needful for both sides.
    My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs

  10. #490

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    Quote Originally Posted by Eudimorphodon View Post
    I've run the Checkit diagnostic on both serial ports and hard disk, both passed.
    Out of curiosity, what version of Checkit are you using on your EX/HX? The last two versions I have tried do not seem to properly start on mine, but works fine on other XT class computers.
    Last edited by rkrenicki; November 10th, 2019 at 01:24 PM.

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