Re: [PARPORT] Simple C prog needed

From: Calle Be (
Date: Fri Jan 10 2003 - 08:44:48 EST

  • Next message: Tim Waugh: "Re: [PARPORT] Simple C prog needed"

    --- Tim Waugh <> wrote:
    > On Thu, Jan 09, 2003 at 04:48:03PM -0800, Calle Be wrote:
    > >
    > > Hi there Joe,
    > >
    > > Many thanx for your answer. Tim's and mine mail volley continued outside of
    > the
    > > mailing list and finally he answered the following:
    > >
    > > echo -ne \\377 | dd of=/dev/port bs=1 seek=$((3*256+7*16+8))
    > >
    > > which I couldn't really follow until your reply. Well, I _still_ doesn't
    > really
    > > follow Tim's line but now it seems I've got myself a better way. Your
    > >
    > > echo -e "\577\c" > /dev/lp0
    > That does a printer handshake (strobe, ack, etc) as well though, which
    > I didn't think you wanted?
    > Tim.

    Well, I want the strobe but not to have to send anything back to the port from
    my device. Here's what the LED display driver information says:

    'Data can be written by setting up a 3 bit binary code on the digit address
    inputs and applying a low level to the WRITE pin.'

    The timing diagram is something like this:

    Address ---\/-----------------------\/-------
     bits ---/\-----------------------/\-------

    WRITE ---------\ ------------
     pin --------------/

    Data ---------------\/---------------\/---

    1. Set the 3 address pins and hold them.
    2. Set WRITE pin low.
    3. Set the 4 data pins and hold then.
    4. Set WRITE pin high.
    5. Now I can't change anything (or so I think)

    Since it's 4 data bits, 3 address bits and one WRITE bit needed, I guess I
    _could_ manage without the printer handshake. Is it the

    echo -ne \\377 | dd of=/dev/port bs=1 seek=$((3*256+7*16+8))

    line I want then? What does the double backslash do? And could you explain the
    seek option a bit more? I've read the man page but don't get that part.

    /Calle Be

    P.S. The data sheet for my LED driver can be found at . I'm gonna use the C/D version.

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