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

  1. #271
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    The prospects for an alternative are of course all the more dire for the EX/HX because not only is the keyboard built in it's just a matrix directly connected to the mainboard. I have a vague memory that there exists some kind of TSR program that helps resolve a few compatibility issues, I'll poke around.

    (Meanwhile, if I really want a dos shell I guess I should dig up a copy of Norton Commander.)

    I have to say I'm flatly amazed at how well the XT-CF works. A number of programs (especially Sierra software) that were neigh unplayable off the floppy emulator are fine running off the CF. (I mean, yeah, 286 CPU would still be great, but...) Even Lemmings plays basically fine.

    Kind of a trip playing this stuff on a computer that I built this much of...

  2. #272
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    Kind of a note to self: I've been mulling this over back and forth, and I think I've about convinced myself I should spring for the additional decoding it'd take to make the flash memory occupy only 32k from C8000-CFFFF instead of taking up the whole C-page. Now that I'm kind of convinced that having UMBs in a 1000EX/HX might actually be useful I think it might be worth reserving some unused memory space for use by other peripherals that want it. (In particular it'd be nice, if such a thing ever exists, to have room for the buffer of a Tandy bus ethernet card without having to disable either half the UMBs or the *only* UMB you get on an HX. It'd also make it possible for this card to coexist with a VGA card for those so inclined.)

    Thinking of piggybacking another 7400 onto the existing one to give me the gates to make it so on the prototype. If nothing else this would be a useful experiment to see if the SMARTWATCH software finds the calendar if it's at x8000, not just x0000.

  3. #273
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    While you're playing around with UMBs, do you have any idea what those little Hi RAM blocks are for? The EX/HX both seem to have a 16K block at BC00h, and my Tandy 1100FD as a 32K block of hi RAM at A800h as well as the 16K block at BC00h.
    IMG_20190830_194246604.jpg
    Forgive the lighting quality. The 1100FD has no backlight and it's even worse without the flash (cellphone cameras suck).
    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. #274
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    Huh, I have no idea why the 1100fd would have anything unusual in that region. It just has a plain CGA video system, right? (Not, say, one of those 400 line systems you found in quite a few laptops and fewer desktops?)

    I was wondering about the phantom RAM at BC000 myself. I believe that when a Tandy 1000 is displaying a 32k-page video mode that's where the second half of the active video page is mapped, but I wasn't sure why it was showing up with only the default 16k allocated. I just now popped into BASIC and did some PEEK and POKE-ing, and I think my verdict is it's a phantom copy of the 16k page at B800. Executing "POKE 1,x" changes the color of the first character cell on the text screen if I set "DEF SEG" to either &HB800 or BC00.
    Last edited by Eudimorphodon; August 30th, 2019 at 10:20 PM.

  5. #275
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    Yeah, it does have CGA (with inverted colors), but I recommend playing games in monochrome if you're epileptic. It changes, either the AC frequency or the voltage (I don't remember which), of the pixel to get the two intermediate shades of the CGA pallet, and the flicker is noticeable.

    Anyways, it would make sense if that extra 16K is for a 32K video page, the display can do 640x200. Question is what the 32K page at A800 is for.

    I believe the 1100FD, rather than taking a hard drive option, used it's internal slot for a 128K hi-RAM card. But documentation on this laptop is scarce, and I've seen neither hide nor hair of a technical manual to get a pinout on that connector. The 1100HD has a 44-pin laptop IDE header, but the 1100FD's internal header is proprietary. If it has the necessary control lines, I'd rather make a CF-card controller instead of a memory board, but either possibility would be open if somebody had a pinout, or at least a schematic. Might just have to probe it out manually (project for later).
    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. #276
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    I believe it's at least theoretically possible to run CF cards in a memory-mapped mode instead of port I/O, but I'm fuzzy on the details. (I've seen minimal 8-bit interfaces using it, I think to do this you need to wire directly to the 50 pin socket, it won't work through a 40 pin adapter.) I don't know if the XTIDE BIOS has any support for this configuration, which takes up... 2k? of address space. Theoretically at least it seems like that could be an option if the connector has non-multiplexed address, data, and memr/memw lines.

  7. #277
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    As you say, I suspect it's just a trunchated XT bus header, but I'd need a pinout to be able to make use of it one way or the other.
    IMG_20190720_180723415.jpgIMG_20190720_180808109.jpg
    Fortunately, this machine comes with 640K onboard, so it's still pretty usable "out of the box."
    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.

  8. #278
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    Quote Originally Posted by Eudimorphodon View Post
    I believe it's at least theoretically possible to run CF cards in a memory-mapped mode instead of port I/O, but I'm fuzzy on the details. (I've seen minimal 8-bit interfaces using it, I think to do this you need to wire directly to the 50 pin socket, it won't work through a 40 pin adapter.) I don't know if the XTIDE BIOS has any support for this configuration, which takes up... 2k? of address space. Theoretically at least it seems like that could be an option if the connector has non-multiplexed address, data, and memr/memw lines.
    In memory mapped mode, you'd address it like a ROM, I think.

    Somebody figured out how to do it for a single board computer http://xetexracing.com/page3/page38/...45/page45.html

    But anyways, that's a project for another day.
    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. #279
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    Quote Originally Posted by blackepyon View Post
    Somebody figured out how to do it for a single board computer http://xetexracing.com/page3/page38/...45/page45.html
    Huh. That's not the way I was thinking of, how he did it. His mapping is actually keeping the card in a mode where it does transfers through a single byte window. (It's clever, though, uses less space.) There's another mode (found it documented in a SanDisk datasheet just now) that presents the currently addressed block in two 512 byte windows (for read and write respectively) that allows you to do address-incrementing block moves, etc, with the CPU. The I/O registers are laid out in the other 1k of space.

  10. #280
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    You don't have to rely on the CF card to do such things. JR-IDE maps the ATA/IDE register map into PC memory space just above the option BIOS and aliases the data register at 512 consecutive address locations in PC memory space. It's so rep movsw can be used to transfer an entire disk block on an 8088 without intermediate instruction fetches slowing it down in a traditional loop.
    "Good engineers keep thick authoritative books on their shelf. Not for their own reference, but to throw at people who ask stupid questions; hoping a small fragment of knowledge will osmotically transfer with each cranial impact." - Me

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