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

Thread: IBM MCA Card Infowindow VGA Control

  1. Default

    Quote Originally Posted by the3dfxdude View Post
    So after some work, I've determined that the card you have is almost certainly NOT a VGA card. The monitor is intended to receive an EGA signal, and accepts the EGA frequencies vsync/hsync through the 9pin port according to the documentation. There was no later model for this monitor specifically made for the PS/2 that gave it VGA functionality. (*the InfoWindow was discontinued not long after the MCA refresh and InfoWindow II is not related at all)

    Anyway, I think it was just IBM marketing at play here. What this card is really is an update of their offering with MCA for PS/2 compatibility. It took the original IBM EGA + Memory Expansion + EGA Jumper card and put it into a single board. Although since it is for a special monitor, it might not be all that useful as an EGA by itself, and really I think the card is going to lack any purpose without the complete system. Indeed, if someone comes across one of these again, they should not part it out as if it's just another IBM PC/XT or PS2.

    Anyhow the reason I decided to reply again here is since I have an IBM PC, with a standard EGA card, I need the EGA jumper card for the sync signal (what the RCA port is for). Could you take a high resolution photo of your InfoWindow VGA card, front and back? I think the purpose of the jumper card was to use the sync signal to activate IRQ 2. I hooked a scope to the sync signal from the monitor, and it appeared that it has some sort of combined horizontal and vertical pulse, I'm guessing from the CRT? If I can figure the signal path from your card, then I could probably recreate the jumper card for its intended purpose.
    There's an old VCFED thread about the jumper card: http://www.vcfed.org/forum/showthrea...Connector-Card

    From the photos in that thread I was able to reverse engineer the jumper card:

    Capture.PNG

    There's a test point in the upper corner of the jumper card. You're supposed to run that over to the IBM GPIB card (which is apparently needed to run the laserdisc player) which has an IRQ jumper block. The jumper wire goes to either IRQ2, IRQ3, or IRQ4.

    What does this whole thing do? Two things: First, it generates a VSYNC signal that is delayed by two horizontal lines. When a feature control bit is turned on, this signal triggers the selected interrupt line. Second, it ties the RCA jack J1 to the EXT_OSC input. There is a register that selects the EGA pixel clock from either 16.257MHz (on the card), 14.318MHz (on the planar), or the EXT_OSC input. Presumably the 4055 provides this as part of the genlock circuit for video overlay purposes.

    Hope this helps.

  2. #12

    Default

    Quote Originally Posted by ejs View Post
    There's an old VCFED thread about the jumper card: http://www.vcfed.org/forum/showthrea...Connector-Card

    From the photos in that thread I was able to reverse engineer the jumper card:

    Capture.PNG

    There's a test point in the upper corner of the jumper card. You're supposed to run that over to the IBM GPIB card (which is apparently needed to run the laserdisc player) which has an IRQ jumper block. The jumper wire goes to either IRQ2, IRQ3, or IRQ4.

    What does this whole thing do? Two things: First, it generates a VSYNC signal that is delayed by two horizontal lines. When a feature control bit is turned on, this signal triggers the selected interrupt line. Second, it ties the RCA jack J1 to the EXT_OSC input. There is a register that selects the EGA pixel clock from either 16.257MHz (on the card), 14.318MHz (on the planar), or the EXT_OSC input. Presumably the 4055 provides this as part of the genlock circuit for video overlay purposes.

    Hope this helps.
    Yes. Thank you.

    I drew up a Kicad schematic a few months back based on that image. I figured I might eventually ask someone to double check the drawing but since you have shared yours, I did just now. Looks like we are in agreement there.

    Thanks for the info on the EGA clock register. I will be watching that when I issues commands to the system.

    If I wasn't clear about this before, the IBM diagnostics disk requires the jumper card installed. It is likely triggering the feature control bit and watching for the interrupt at startup. It will not continue without the card. I don't think it should need the clock to perform the other functions, but when programming the thing using the IBM library, you issue a start command to the display unit, to be able to drive the functions on the display. It is likely there is a negotiation with the jumper card which eventually may lead to switching from the internal oscillator to the external oscillator. Hopefully this works with my clone EGA card. I guess that explains why it calls the sync a dot clock in some places in the documentation.

    The monitor uses GPIB to communicate with the computer.

    I'll be gathering the parts and checking how this works and integrating in time. If there is something about operating it that I can't figure out, I'll open a new 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
  •