NAME
        port_handler -- standard serial/parallel/printer port handler.

   SYNOPSIS
        Open("PRT:[RAW/TRANSPARENT/UNIT=<Unit number>]",...);

        Open("SER:[BAUD=<speed>/CONTROL=<settings>/UNIT=<Unit number>]",...);

        Open("PAR:[UNIT=<Unit number>]",...);

   FUNCTION
        Port-handler allows AmigaDOS to interface to a standard parallel
        device, a standard printer device, and a standard serial device.

        Accessing "PAR:" connects AmigaDOS to the system's parallel port.
        By default this will use parallel.device, unit 0. To use a
        different unit number, such as 1, specify "PAR:UNIT=1" instead.

        Accessing "PRT:" connects AmigaDOS to the system's printer. Data
        written to PRT: is processed by the Amiga's printer device, handling
        conversions of ANSI sequences, and sent to the printer. Accessing
        "PRT:RAW" instead causes carriage return translation to be turned
        off in the printer device while printing. To send data transparently
        to the printer, without any translation or escape sequence substitution
        whatsoever, use "PRT:TRANSPARENT". The TRANSPARENT and RAW switches
        are mutually exclusive. By default "PRT:" will access printer.device,
        unit 0. To use a different unit number, such as 1, specify "PRT:UNIT=1"
        instead. The keywords can be combined, such as in "PRT:RAW/UNIT=1".

        Accessing "SER:" connects AmigaDOS to the system's default serial port.
        Following SER:, the baud rate and some control information can be
        supplied. This is done in the form "SER:baud/control" where baud is
        a number indicating the baud rate, and where control is a 3 letter
        sequence denoting the number of read/write bits, the parity, and the
        number of stop bits. For example, "SER:9600/8N1" connects to the
        serial port, sets the baud rate to 9600, with 8 bit data, no parity,
        and 1 stop bit. The possible control settings are:

                1st character: 7 or 8
                2nd character: N (No parity), O (Odd parity), E (Even parity)
                               M (Mark parity), S (Space parity)
                3rd character: 1 or 2

        Specifying no baud rate or control values when accessing SER: gives you
        the values set in Serial preferences.
        To override the default unit number, use the UNIT keyword, as with the
        PRT: and PAR: devices described above. For example, to access unit 1
        with 38400 bps you could use "SER:38400/UNIT=1".

   PACKETS
        ACTION_FINDINPUT
        ACTION_FINDOUTPUT
        ACTION_FINDUPDATE
        ACTION_READ
        ACTION_WRITE
        ACTION_END
        ACTION_IS_FILESYSTEM

   MOUNTLIST ENTRIES
        dos.library automatically mounts PAR:, PRT:, and SER: upon
        system boot up. The mount entries used by dos.library are equivalent
        to:

           SER:    Handler   = L:Port-Handler
                   Priority  = 5
                   StackSize = 800
                   GlobVec   = 1
                   Startup   = 0
           #

           PAR:    Handler   = L:Port-Handler
                   Priority  = 5
                   StackSize = 800
                   GlobVec   = 1
                   Startup   = 1
           #

           PRT:    Handler   = L:Port-Handler
                   Priority  = 5
                   StackSize = 1000
                   GlobVec   = 1
                   Startup   = 2
           #

        Starting with V40, you can also provide disk-based mount entries
        which let you use port-handler as a serial handler on various devices
        and units. The form of these mount entries is:

           SER0:   EHandler  = L:Port-Handler
                   Priority  = 5
                   StackSize = 800
                   GlobVec   = 1
                   device    = serial.device
                   unit      = 0
                   Flags     = 0
                   Control   = "8N1"
                   Baud      = 9600
        #

        The "Device", "Unit" and "Flags" keywords define the parameters
        that the handler uses for opendevice(). "baud" and "control"
        define the default values for baud rate and control information for
        whenever that serial handler is accessed by name only, without
        explicit baud rate and control information specified.

   NOTE
        Prior to V40, the baud rate and control information for SER: were
        only recognized if an A2232 multi-serial card was installed in the
        system. Starting with V40, these values are always recognized.

        The TRANSPARENT, UNIT, BAUD and CONTROL keywords were introduced
        with Port-Handler V44. For the different devices, the argument
        templates are:

            PRT:RAW/S,TRANSPARENT/S,UNIT/K/N
            SER:BAUD/N,UNIT/K/N,CONTROL/F
            PAR:UNIT/K/N

        Instead of blank spaces, keywords must be separated by slashes ("/").