parallel(HW)                    19 June 1992                    parallel(HW)


 Name

    parallel - parallel interface devices

 Description

    There are several parallel devices:

    /dev/lp0  Main parallel adapter

    /dev/lp1  Adapter on monochrome video card

    /dev/lp2  Alternate parallel adapter (on appropriate machines)

    It is not possible to have all three parallel devices on one system.
    Some AT computers allow the use of two parallel devices, /dev/lp2, and
    either /dev/lp0 or /dev/lp1.

    If a parallel device fails to interrupt properly, the parallel driver
    enters ``poll mode''.  Once interrupts are received from the device, the
    driver returns to its original mode.

    The parallel driver delays a certain amount of time when a parallel de-
    vice is closed.  The amount of delay can affect printer performance, but
    is necessary to compensate for different sizes of printer buffers and
    printer speeds.  For example, this command sets the delay on close to 1
    second, specified in tenths of a second:

       stty time 10< /dev/lp0

    When given from a prompt, this command will only work if the port is
    open. It is recommended that a variation of this command be placed in the
    interface script used with the parallel device to achieve the same
    results:

       stty time 10 0< &1

 Notes

    Parallel adapters on add-on cards will function, but switches must be set
    correctly.  Some compatible computers have ports LP0 and LP1 reversed.

    The stty(C) command for output processing is supported on a parallel de-
    vice.  stty options that have no effect on a parallel device are ignored
    and no error messages are displayed.

 Usage

    Usually invoked by lp(C), but can be written to directly.

 Files

    /dev/lp0
    /dev/lp1
    /dev/lp2

 See also

    lp(C), lp(HW), lpadmin(ADM), lpsched(ADM), serial(HW)