[PARPORT] LCD problem

From: Bart De Win (bart.dewin@cs.kuleuven.ac.be)
Date: Thu Sep 07 2000 - 08:10:54 EDT

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    I'm new to this list and in the description of the list I read that this list
    deals with device drivers. This is not really a driver question, so I hope
    it is acceptable.

    At home, I'm building an MP3 player. I bought an 20x4 LCD display and
    connect it through the parallel port. I wrote some code to control the
    display. All worked fine on my previous computer. Recently though I bought
    a Bookpc (www.pcchips.nl) and I tried to use the LCD through its parallel
    port and this is were my problem is situated.

    For my previous PC, I had to configure the BIOS for EPPECP version 1.7. The
    BIOS of my bookpc doesn't support that version change. I suppose it only
    supports version 1.9. I don't understand why I had to configure my previous
    computer to EPPECP, because as far as I know I don't use any features of
    EPP/ECP. For the LCD display I simply have to put data on the data lines and
    then I have to set the Enable line on the LCD to high and later to low again
    (this acts as a strobe). This is all the functionality I'm using, so I think
    I don't need EPP/ECP.

    When I boot my bookpc, the parallel port driver says that my parallel port
    (at 0x378) supports the following modes : SPP, EPP, ECP, ECPEPP, ECPPS2
    I can restrict this when I change the parallel port settings in the BIOS.
    I tried all possible modes in BIOS and my LCD still doesn't show anything.

    When I write something to address 0x378 I can see through a cable tester that
    it actually goes through the port. But nothing happens on the LCD.

    I read somewhere that it is important to set the mode of the parallel port
    before using it. So I tried to set the ECR (at address 0x378+0x402) to 0x1F,
    which should be Standard Mode. But when I read the ECR afterwards, I get the
    value 0xFF, so it seems that the ECR is not changed. (By The Way, to do this
    I had to ask permissions to the Linux kernel through the iopl() call.)

    I don't know which parallel port chip I'm using. I asked the manufacturer
    for more detailed specs of the motherboard, but I have not yet received
    anything. So I don't know if for example the ECR is always located at
    Base_Address + 0x402.

    To recapitulate : I'm clueless. I don't know what to test anymore. Maybe
    I'm missing a crucial detail somewhere ... Has anyone of you guys more
    experience in this matter ?

    And maybe another question : since I write directly to the address of the
    parallel port, do I actually need the parport_pc driver to be loaded ? If so,
    why ?

    Sorry for this rather long mail.

    Best regards,
    Bart De Win.

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