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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
    For what it's worth, I've assembled a specimen of my new RAM/ROM card and initially tested it in both the EX and the Frankenstein HX and so far it looks like the PCB is correct. (Planning to shoot a video about the HX... thing, I have now. I've been busy.)

    Word of advice if anyone is using an ST-flash based design instead of EEPROM for their bios chip: the Lotech flash utility hangs under DOS 2.1. Apparently I didn't suss that out the last time so I burned some cycles on swapping flash chips between cards before I figured that out. :b

    Also, apparently Mister Black didn't get the only bum RAM chips from eBay. I wish I had a PCjr to try them in, they've been sitting around way too long to return. Feh.

    Leave a comment:


  • dJOS
    replied
    Originally posted by blackepyon View Post
    Ah! I was wondering what those were for. of course, you need to open the chassis for that...
    Does it interfere with anything if you leave it closed?
    On the EX, the pins are right next to the PLUS expansion slot and even have the pins installed (at least on mine they were). You can prolly get to them even without removing the crappy sheilding.

    If you leave them Open (default), they put +5v onto that pin.

    Leave a comment:


  • blackepyon
    replied
    Originally posted by dJOS View Post
    You can enable nibble mode by closing the E1-E2 pins with a jumper on the EX/HX which connects the printer select line and gives you limited birectional funtion.
    Ah! I was wondering what those were for. of course, you need to open the chassis for that...
    Does it interfere with anything if you leave it closed?

    Leave a comment:


  • dJOS
    replied
    Originally posted by blackepyon View Post
    Interesting idea. The onboard parallel port is not bi-directional, so far as I know, so you'd only be able to "receive" using the status port (5 bits, one of them inverted), not the data port. But it could be done.
    You can enable nibble mode by closing the E1-E2 pins with a jumper on the EX/HX which connects the printer select line and gives you limited birectional funtion.

    Leave a comment:


  • blackepyon
    replied
    Originally posted by bladamson View Post
    It could be used for any sort of geek port, but I plan to plug it into the GPIO header of a raspberry pi. I want to eventually try to write a DOS packet driver bridged to the pi's ethernet, and I also want to make the PC filesystems available to the Pi (and vice versa).

    I suppose I could just use a 4-bit PLIP connection to the existing parallel port, but that would be slower and less cool. :3 This way I can mount the Pi to the card and it'll be all pretty internal expansion thingy without some ugly stuff hanging out on ribbon cables.
    Interesting idea. The onboard parallel port is not bi-directional, so far as I know, so you'd only be able to "receive" using the status port (5 bits, one of them inverted), not the data port. But it could be done.

    Leave a comment:


  • bladamson
    replied
    Originally posted by blackepyon View Post
    What are you using the 8255 for?
    It could be used for any sort of geek port, but I plan to plug it into the GPIO header of a raspberry pi. I want to eventually try to write a DOS packet driver bridged to the pi's ethernet, and I also want to make the PC filesystems available to the Pi (and vice versa).

    I suppose I could just use a 4-bit PLIP connection to the existing parallel port, but that would be slower and less cool. :3 This way I can mount the Pi to the card and it'll be all pretty internal expansion thingy without some ugly stuff hanging out on ribbon cables.

    Leave a comment:


  • Eudimorphodon
    replied
    I've run both 2 and 3 with no apparent problem. (At one point I was wondering if there might be some incompatibility with 3.0 because I would intermittently get errors on the extended RAM test that I didn't get on 2.0 and the phrasing of the error kind of implied it might be trying to read a register for parity errors that the Tandy 1000 doesn't have, but it turned out to be a loose chip socket.)

    I don't remember if 2.0 ran in 256k or not, I guess I could check.

    Leave a comment:


  • blackepyon
    replied
    Originally posted by rkrenicki View Post
    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.
    I've been using Checkit 3. The caveat is that it requires more than the base 256K of RAM, so it'll only work if you're got the memory expansion working. Checkit version 1 works just fine on 256K.

    Leave a comment:


  • rkrenicki
    replied
    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 10, 2019, 01:24 PM.

    Leave a comment:


  • Eudimorphodon
    replied
    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.

    Leave a comment:


  • blackepyon
    replied
    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?

    Leave a comment:


  • bladamson
    replied
    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?

    Leave a comment:


  • bladamson
    replied
    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.

    Leave a comment:


  • blackepyon
    replied
    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.

    Leave a comment:


  • dJOS
    replied
    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.

    Leave a comment:

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