Image Map Image Map
Page 3 of 5 FirstFirst 12345 LastLast
Results 21 to 30 of 50

Thread: Where Can I purchase a Tandy 1000 EX RAM Board (Plus Board) ?

  1. #21
    Join Date
    Mar 2015
    Location
    Vancouver Island, BC, Canada
    Posts
    4

    Default

    Here are a few photos of a Tandy 1000 HX with memory expansion board, homemade ISA adapter cable, and Lo-tech ISA CompactFlash adapter: http://imgur.com/a/ZJgP5

    Some quick measurements of the HX/EX memory expansion board:
    The 62-pin connector on the memory expansion card is 10 mm from the side of the PCB (photo 13), and 20 mm from the back of the PCB (photo 14). The bracket is 5 mm past the back edge of the PCB (photo 14). The PCB is 146 mm long, 105 mm wide (photo 15). I'm happy to take more measurements if helpful.

    I'm very happy with the Lo-tech ISA CompactFlash adapter, and also very impressed with the other boards I bought from Lo-tech. I would definitely buy a couple of any expansion boards made available - memory expansion, riser card, a multifunction card - I would love to see any of these!

    Is there any use for DMA in a Tandy 1000 HX / EX? Or would a memory expansion board without a DMA controller be fully functional? Would the Lo-tech 1MB RAM Board work just as well as the Tandy 1000 HX/EX memory + DMA board?

  2. #22
    Join Date
    Mar 2006
    Location
    Massachusetts, USA
    Posts
    1,889

    Default

    For a memory board, Tandy used eight 256kx1 and four 64kx4 chips. You can cut that chip number in half by using 256kx4 chips. That will allow more room for a discrete 8237 DMA chip and the logic necessary to interface the chip to the bus. You can also loose the short connector next to the VLSI chip and just use one connector at a more standard height. Even so, I think it would take some custom logic due to the lack of space.

    A clock would be a nice thing to have, it could go on the serial board.

    The EX already has a parallel port and fitting a large connector onto a bracket will be tricky.
    My Retro Computing and Vintage Gaming Blog : http://nerdlypleasures.blogspot.com/

  3. #23
    Join Date
    Feb 2012
    Location
    Northern Nevada
    Posts
    698

    Default

    Quote Originally Posted by Great Hierophant View Post
    For a memory board, Tandy used eight 256kx1 and four 64kx4 chips. You can cut that chip number in half by using 256kx4 chips. That will allow more room for a discrete 8237 DMA chip and the logic necessary to interface the chip to the bus. You can also loose the short connector next to the VLSI chip and just use one connector at a more standard height. Even so, I think it would take some custom logic due to the lack of space.

    A clock would be a nice thing to have, it could go on the serial board.

    The EX already has a parallel port and fitting a large connector onto a bracket will be tricky.
    I just discovered yesterday, browsing on Tandy's doc site, there was a second memory expansion board that came with 512k RAM installed, and a driver to use 128k as a RAMdisk (as the system would then have 768k RAM). The part number ended in 2062, instead of 1062 like the other RAM board.

    If that 128k was a high memory area useable by himem.sys, that would be very useful....

    Also, I have an aftermarket DMA/RAM board in my 1000EX, that doesn't have the CPLD the Tandy card does. I'll get some photos of it, it may be easier to clone.

  4. #24
    Join Date
    Mar 2011
    Location
    Atlanta, GA, USA
    Posts
    1,576

    Default

    I'm not sure why you would need DMA. The only application of it is to speed up floppy transfers.

    Likewise it would be silly to add DRAMs to any reproduction when 512Kx8 SRAMs are so plentiful now.

    One could adapt something like a JR-IDE design to a PLUS form factor. Maybe drop the POST and 2nd SRAM for a DUART instead. DMA is a bit faster than memory mapped I/O. But it's a difference of 330KB/s vs at best 400KB/s. A comparison akin to which super car should Grandma drive...
    "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

  5. #25
    Join Date
    Mar 2015
    Location
    Vancouver Island, BC, Canada
    Posts
    4

    Default

    Quote Originally Posted by eeguru View Post
    I'm not sure why you would need DMA. The only application of it is to speed up floppy transfers.
    Should DOS (or the BIOS?) detect that DMA is available, and start using it, if the memory expansion board is installed? Is there a benchmark or diagnostics I can run to see that DMA is available and compare floppy transfer speed?

    I tried a simple test of timing how long it takes to copy some files from floppy disk and didn't see any difference whether the memory expansion board is installed or not. (using the "Tandy 1000 EX Memory Expansion Board cat. no. 25-1062")

  6. #26
    Join Date
    Oct 2009
    Location
    Huntsville, AL
    Posts
    1,256

    Default

    Quote Originally Posted by HoJoPo View Post
    I just discovered yesterday, browsing on Tandy's doc site, there was a second memory expansion board that came with 512k RAM installed, and a driver to use 128k as a RAMdisk (as the system would then have 768k RAM). The part number ended in 2062, instead of 1062 like the other RAM board.

    If that 128k was a high memory area useable by himem.sys, that would be very useful....

    Also, I have an aftermarket DMA/RAM board in my 1000EX, that doesn't have the CPLD the Tandy card does. I'll get some photos of it, it may be easier to clone.
    I made a half hearted attempt to modify the plus memory board I had in my HX to support 768kB. In theory it should be possible as the same ASIC is used on the Tandy 1000TX. It used a different combination of DRAMs in each bank. Details are in the hardware reference manual for the 1000HX, and the associated strapping modes. I tried ripping out the 64k DRAMs and replacing them with a bank of 256k DRAMs piggybacked on the ones that were on the system and then tying back the RAS/CAS signals to the 64k dram bank's ras/cas lines and changing the strapping to match the TX. System wouldn't boot. Not sure if that's a BIOS issue or a problem with my wiring. Ended up putting it back without too much further troubleshooting.

  7. #27
    Join Date
    Mar 2011
    Location
    Atlanta, GA, USA
    Posts
    1,576

    Default

    Quote Originally Posted by baudfiend View Post
    I tried a simple test of timing how long it takes to copy some files from floppy disk and didn't see any difference whether the memory expansion board is installed or not. (using the "Tandy 1000 EX Memory Expansion Board cat. no. 25-1062")
    Then I'm not sure how any DMA function on-board the Tandy ASIC is being used. It is wired to cpu hold, hold ack, and the DMA request and ack lines for floppy. You can have all the hardware acceleration support, but if there is no software support..... ? Even if it could move data to/from other peripherals, I'm not aware of any driver with support. It's primary function is obviously to provide refresh control for the local DRAM. Maybe Tandy never got around to anything else?
    "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

  8. #28
    Join Date
    Aug 2006
    Location
    Chicagoland, Illinois, USA
    Posts
    6,443
    Blog Entries
    1

    Default

    Without DMA, the Tandy and PCjr disables interrupts for large chunks of time in order to transfer data to/from the drives. If you're just sitting at DOS there is not much of a speed difference, but without interrupts, attempting to write to disk while something else is happening does not go well. The classic application of this is trying to transfer files over serial/modem; on systems without DMA, there was a practical maximum speed (2400 baud or lower) before bits were dropped. The interim solution was to download to a RAM disk, then transfer to physical disk later.
    Offering a bounty for:
    - A working Sanyo MBC-775, Olivetti M24, or Logabax 1600
    - Music Construction Set, IBM Music Feature edition (has red sticker on front stating IBM Music Feature)

  9. #29
    Join Date
    Oct 2009
    Location
    Huntsville, AL
    Posts
    1,256

    Default

    In addition to what Trixter mentions, the PLUS memory card also supplies DMA channel lines to the two passthrough PLUS card connectors, basically making the PLUS connector look pretty much like a regular 8-bit ISA slot with a 1:1 pin mapping.

  10. #30
    Join Date
    Mar 2006
    Location
    Massachusetts, USA
    Posts
    1,889

    Default

    Quote Originally Posted by Trixter View Post
    Without DMA, the Tandy and PCjr disables interrupts for large chunks of time in order to transfer data to/from the drives. If you're just sitting at DOS there is not much of a speed difference, but without interrupts, attempting to write to disk while something else is happening does not go well. The classic application of this is trying to transfer files over serial/modem; on systems without DMA, there was a practical maximum speed (2400 baud or lower) before bits were dropped. The interim solution was to download to a RAM disk, then transfer to physical disk later.
    At least it is not as bad as it is on the PCjr., where decoding the keyboard bit stream by the CPU required interrupts to be disabled for a long time. The Tandys have a proper serial register and should not have this conflict. However, one should not expect keys to be registered while the disk drives are active.
    My Retro Computing and Vintage Gaming Blog : http://nerdlypleasures.blogspot.com/

Tags for this Thread

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •