Image Map Image Map
Page 1 of 2 12 LastLast
Results 1 to 10 of 13

Thread: Compaq Deskpro M - how to change the parallel port mode

  1. #1

    Default Compaq Deskpro M - how to change the parallel port mode

    I've been into the EISA configuration and you can change the port (3BC/378/278 ) and the resources, but no place to change the type such as SPP/bidirectional/EPP/ECP. It does show a DMA channel as one of the options, so I would think it supports ECP, but maybe it is pre-official ECP or something? I wrote a test program that detects the port mode based on the "parallel port complete" book and it works great on the Compaq N400C notebook I have matching all 4 modes I set in the BIOS. On the deskpro M though (486/66), it always comes up SPP. It began at 3BC and I moved it to 378. Then I disabled the DMA channel because I saw a page say that would push it out of ECP mode into EPP mode, but it stays SPP as far as my detection goes.

  2. #2
    Join Date
    Jan 2007
    Location
    Pacific Northwest, USA
    Posts
    34,929
    Blog Entries
    18

    Default

    Some SPP implementations still observe bit 5 in the control register as switching off the data drivers. Have you tried that?

  3. #3

    Default

    Yes. The test method is detect if is an ECP, then see if it is an EPP, if neither, then can you read/write to its data port (SPP), then set bit 5 in the Control Register and see if it still changes when you read/write to the data port.

  4. #4
    Join Date
    Jan 2007
    Location
    Pacific Northwest, USA
    Posts
    34,929
    Blog Entries
    18

    Default

    Deskpro M--is that the 486 CPU on a card EISA model? It may simply be too old to support ECP/EPP.

  5. #5

    Default

    Yes. I wonder if you are right. It does have a DMA option that can be set for the parallel port however. Could it be something pre-ECP/EPP?

  6. #6
    Join Date
    Jan 2007
    Location
    Pacific Northwest, USA
    Posts
    34,929
    Blog Entries
    18

    Default

    Could well be--I don't know much about that particular model.

  7. #7
    Join Date
    Mar 2017
    Location
    New Jersey, USA
    Posts
    588

    Default

    A basic Deskpro/M system had 3 main cards: there was the EISA bus card which had all the slots, a CPU card that plugged into a special CPU slot on the EISA bus card, and an I/O card that connected to the edge of the EISA bus card. There were 2 variants of the I/O card, one was just basic I/O (serial, parallel, keyboard, mouse, floppy, IDE and system ROM), and the other added audio support to all that. Available CPU cards included 386 (25 and 33MHz), 486SX (16/25/33), 486DX (33), 486DX2 (50/66), and Pentium (60/66). The EISA bus card also had a special memory expansion slot but CPU cards came with some RAM so a memory card wasn't mandatory. You did need to include a video card, however, video was not included on the I/O card, so a minimal system would be 4 cards.

    I don't happen to recall whether Compaq made any claims about the parallel port capability, but I believe the /M series was introduced in 1991. If EPP also was announced in 1991, and ECP in 1992, it's unlikely the original I/O card would have included it.

  8. #8
    Join Date
    Jan 2007
    Location
    Pacific Northwest, USA
    Posts
    34,929
    Blog Entries
    18

    Default

    Er, every PS/2 had EPP (bidirectional) capabilities, which dates from 1987.

  9. #9

    Default

    This parallel port is on the IO board (if that is what it is called). It is a horizontal port on the back under the power supply, not in a card. The system does have its processor on a card though. I find it interesting that it has a DMA option for the parallel port, but maybe it follows its own specification and an official ECP/EPP. You would think with how well Compaq documented things that there would be a technical document somewhere for it though. I'll try to probe the possible ports for it later and see if I can find something there even if it doesn't follow ECP/EPP spec.

  10. #10
    Join Date
    Mar 2017
    Location
    New Jersey, USA
    Posts
    588

    Default

    every PS/2 had bidirectional parallel ports, but I found a web page claiming that the name "EPP" was coined by Intel, Xircom and Zenith in 1991, and that ECP was introduced by Microsoft and HP in 1992. Then in 1994 IEEE-1284 tried to include all three, EPP, ECP and SPP (regular PS/2 bidirectional). I would not be at all surprised to hear that EPP, ECP, or both were based on existing practice from IBM (certainly) and Compaq (probably).

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
  •