NAME
        open -- a request to open the parallel port

   SYNOPSIS
        error = OpenDevice("parallel.device", unit, ioExtPar, flags)
        D0                  A0                D0    A1        D1

   FUNCTION
        This function allows the requestor software access to the parallel
        device.  Unless the shared-access bit (bit 5 of io_ParFlags) is
        set, exclusive use is granted and no other access is allowed
        until the owner closes the device.

        A FAST_MODE, can be specified (bit 3 of io_Parflags) to speed up
        transfers to high-speed printers. Rather than waiting for the printer
        to acknowledge a character using the *ACK interrupt, this mode will
        send out data as long as the BUSY signal is low. The printer must be
        able to raise the BUSY signal within 3 micro-seconds on A2630s,
        otherwise data will be lost. Should be used only in an exclusive-
        access open().

        A SLOWMODE mode can be specified (bit 4 of io_ParFlags) when very
        slow printers are used. If the printer acknowledges data at less
        than 5000 bytes per second, then this mode will actually save CPU
        time, although it consumes much more with high-speed printers.

        The PTermArray of the ioExtPar is initialized only if the EOFMODE
        bit (bit 1 of io_ParFlags) is set. The PTermArray can be further
        modified using the pdcmd_setparams command.

   INPUTS
        "parallel.device" - a pointer to literal string "parallel.device"
        unit - Must be zero for future compatibility
        ioExtPar - pointer to an IO request block of structure ioextpar to
                   be initialized by the open() function. the io_parflags
                   field must be set as desired.
        flags - Must be zero for future compatibility

   RESULTS
        d0 -- same as io_Error
        io_Error -- if the open succeded, then io_error will be null.
                    If the open failed, then io_error will be non-zero.

   SEE ALSO
        exec/closedevice()