Image Map Image Map
Page 6 of 8 FirstFirst ... 2345678 LastLast
Results 51 to 60 of 72

Thread: Trident VGA and IBM PC

  1. #51
    Join Date
    Jul 2010
    Location
    Silicon Forest, Oregon, USA
    Posts
    664

    Default

    Quote Originally Posted by Vic3Dexe View Post
    You can extend ALE to the front of /MRD signal (as Tronix did).
    Or just use front of /MRD to latch address - I think this will also work.
    I implemented an easier approach - it only uses ALE and AEN signals.
    I believe this approach is also more reliable. It doesn't change ALE (other than adding a slight delay) when AEN is inactive, and therefore it will not break AT systems. (Most likely Tronix's schematic will not work on an AT in 16-bit slot, because LA17-LA23 will not be valid when /MEMR or /MEMW are activated).

  2. #52

    Default

    Some people reported ultra light solution - just pull up TVGA9000 ALE pin to +5V....

  3. #53

    Default

    Quote Originally Posted by Tronix View Post
    Some people reported ultra light solution - just pull up TVGA9000 ALE pin to +5V....
    Cool! I assume you do this with a resistor as always?

    This trick would be useful to get this working on any XT I have in the future; but does the TVGA8900D/9000 chipset have any compatibility with the Olivetti M24's byteswapped BIU implementation? I fear it's what breaks most "XT compatible" video cards from VGA and up on this machine.
    Join the penny pincher army today!

  4. #54
    Join Date
    Jul 2010
    Location
    Silicon Forest, Oregon, USA
    Posts
    664

    Default

    Quote Originally Posted by Tronix View Post
    Some people reported ultra light solution - just pull up TVGA9000 ALE pin to +5V....
    Huh, tested this on the boards I have available: IBM PC, IBM XT, PC-Retro, a chipset-based Turbo XT, 286-AT, and it works perfectly.
    Apparently Trident TVGA has transparent latches on the address lines, tying ALE pin high keeps these latches in "transparent" mode, and it works as long as the address remains valid during I/O or memory operation.

    That's indeed a very easy fix.

  5. #55
    Join Date
    Jul 2010
    Location
    Silicon Forest, Oregon, USA
    Posts
    664

    Default

    Quote Originally Posted by Kazblox View Post
    Cool! I assume you do this with a resistor as always?
    Resistor is not needed (but won't hurt), just disconnect TVGA ALE pin from ISA, and connect it to +5V.

    does the TVGA8900D/9000 chipset have any compatibility with the Olivetti M24's byteswapped BIU implementation? I fear it's what breaks most "XT compatible" video cards from VGA and up on this machine.
    I don't think it is something that a VGA chipset could possibly fix it. The problem is that VGA registers are accessed by writing register index to a lower byte of a 16-bit port and value to the higher byte. If bytes are swapped, it will write the value first... (likely to the wrong register)
    Last edited by sergey; November 16th, 2017 at 09:22 AM.

  6. #56

    Default

    Well, most, if not all Tseng ET4000 cards somehow manage to maneuver this bug. I don't know how, as I never looked into tracing the problem myself.
    Join the penny pincher army today!

  7. #57

    Default

    Does the card still work fine in XT/AT etc with TVGA ALE tied high?

    - Gary

    Quote Originally Posted by sergey View Post
    Resistor is not needed (but won't hurt), just disconnect TVGA ALE pin from ISA, and connect it to +5V.

  8. #58
    Join Date
    Jan 2012
    Location
    Raleigh, NC, USA
    Posts
    467

    Default

    Quote Originally Posted by sergey View Post
    Resistor is not needed (but won't hurt), just disconnect TVGA ALE pin from ISA, and connect it to +5V.
    Will this fix allow your SVGA card to work with the IBM XT 5160?

    Thanks!

    Heather

  9. #59
    Join Date
    Jul 2010
    Location
    Silicon Forest, Oregon, USA
    Posts
    664

    Default

    Quote Originally Posted by SkydivinGirl View Post
    Will this fix allow your SVGA card to work with the IBM XT 5160?

    Thanks!

    Heather
    Yes, that makes the card work in IBM PC, IBM XT, and compatibles.
    On my board, I put a piece of tape to cover the ALE pad on the ISA connector - 4th pad from the right, when looking at the back side of the board, and then I soldered a piece of wire between pin 19 (VCC) and pin 21 (ALE) of the TVGA9000I ICs:
    TVGA-ALE_Fix.jpg

  10. #60
    Join Date
    Jan 2012
    Location
    Raleigh, NC, USA
    Posts
    467

    Default

    That's really great news! Your card worked perfectly in my Commodore PC10-III but wouldn't work at all in the 5160. Hopefully I'll have time to mod my card this weekend. I'll report back with the results.

    Heather

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
  •