Image Map Image Map
Page 2 of 2 FirstFirst 12
Results 11 to 13 of 13

Thread: Overclocking a Tandy 1000 EX: ever been done?

  1. #11
    Join Date
    May 2011
    Location
    Outer Mongolia
    Posts
    1,269

    Default

    Quote Originally Posted by CarlosTex View Post
    Which OSC frequency is sent to the CPU? For the Tandy EX i assume its a 14.318MHZ signal, which /3 gives 4.77 and /2 gives 7.15Mhz.

    So to maximize the V20HL potential you need to feed the light blue chip with 32MHz. /3 will give a slow speed of 10,66 and /2 will give full CPU 16Mhz potential. The issue is if the light blue chip has a single 14.318MHz input, patching a higher clock signal into that will screw up the other signals. Check the light blue chip pinout.
    I laid it out earlier, but, yeah, the issue is I can't feed an alternative frequency into light blue for just the CPU, it's completely different from the timing chip in the SL. A single 28 mhz clock is the source for everything in the system other than the disk controller. This looks like a far harder job than the SL.

    I was trying to find a datasheet for Light Blue to see if it would help me figure out what signals it handles that actually need to be synchronous (I mentioned the handling of the Ready signal as something that stood out as a red flag) but as of yet no luck. My thought at this point is this probably won't work without external circuitry to divorce some functions from Light Blue's built-in circuity.

  2. #12

    Default

    Yes this seems like a hard task. You might need to design an independent clock circuit exclusively for the CPU, there might be no way out of it.

    Sometimes it seems that you're so close but it is not possible. I've been looking today and i found out that the Tandy 1000 SL and TL are pretty much the same in terms of I/O ports. With a hardware mod it might be possible to upgrade the SL to 768Kb of memory just like the TL's and RL's.

    My last pet peeve on overclocking Tandys would be on a Tandy 1000 TL. I think it would be as easy as my SL, short of replacing the CPU, RAM and DMA controller and of course the crystal mod. A 286 running at 16Mhz on the TL and combining it with an EGA card would make a TL quite an interesting machine. I need to find a TL motherboard first.
    Last edited by CarlosTex; August 15th, 2019 at 11:53 AM.

  3. #13
    Join Date
    May 2011
    Location
    Outer Mongolia
    Posts
    1,269

    Default

    So I did just find a datasheet (of sorts, it's pretty minimal) for Light Blue; it's in the PDF of the 1000 HX manual that's floating around the web.

    Honestly about the only strategy I can think of based on the block diagram in there *might* be to free the 14mhz, 4.77mhz (there's an independent 4.77 mhz clock that's always there regardless of the state of CPUCLK) and 3.58mhz clock outputs and provide them from a new, independent clock divider running off the 28mhz crystal, and *then* feeding Light Blue with a faster clock in place of the 28mhz line. That *might* work to make the system more equivalent to how the SL works? The block diagram shows the "control signal generator" is connected to CPUCLK internally, and that seems to be where all those duty cycles that are going to be messed up by just pinning a faster clock to the CPU clock input are synthesized. (And since its connection to CPUCLK is internal to the silicon rather than the clock generator and control signal generator being separate chips we're kind of boned.)

    Assuming there's no *external* dependency on anything driven by the 14, 4.77, and 3.58mhz being synchronous with the CPU cycles maybe that could work? I think I need to up my electronics game a little bit before I can design it, but I guess in theory you might be able to implement it on some kind of interposer board that sticks in the Light Blue socket.

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
  •