The printer device operates like the other Amiga devices.  To use it, you
must first open the printer device, then send I/O requests to it, and then
close it when finished.  See the introduction to amiga devices chapter
for general information on device usage.

There are three distinct kinds of data structures required by the printer
I/O routines. Some of the printer device I/O commands, such as cmd_start
and cmd_write require only an iostdreq data structure. others, such as
prd_dumprport and prd_prtcommand, require an extended data structure
called IODRPReq (for "Dump a RastPort Request") or IOPrtCmdReq (for
"Printer Command Request").

For convenience, it is strongly recommended that you define a single data
structure called printerIO, that can be used to represent any of the three
pre-defined printer communications request blocks.

    union printerIO
    {
        struct IOStdReq    ios;
        struct IODRPReq    iodrp;
        struct IOPrtCmdReq iopc;
    };

    struct IODRPReq
    {
        struct  Message io_Message;
        struct  Device  *io_Device;     /* device node pointer  */
        struct  Unit    *io_Unit;       /* unit (driver private)*/
        UWORD   io_Command;             /* device command */
        UBYTE   io_Flags;
        BYTE    io_Error;               /* error or warning num */
        struct  RastPort *io_RastPort;  /* raster port */
        struct  ColorMap *io_ColorMap;  /* color map */
        ULONG   io_Modes;               /* graphics viewport modes */
        UWORD   io_SrcX;                /* source x origin */
        UWORD   io_SrcY;                /* source y origin */
        UWORD   io_SrcWidth;            /* source x width */
        UWORD   io_SrcHeight;           /* source x height */
        LONG    io_DestCols;            /* destination x width */
        LONG    io_DestRows;            /* destination y height */
        UWORD   io_Special;             /* option flags */
    };

    struct IOPrtCmdReq
    {
        struct  Message io_Message;
        struct  Device  *io_Device;     /* device node pointer  */
        struct  Unit    *io_Unit;       /* unit (driver private)*/
        UWORD   io_Command;             /* device command */
        UBYTE   io_Flags;
        BYTE    io_Error;               /* error or warning num */
        UWORD   io_PrtCommand;          /* printer command */
        UBYTE   io_Parm0;               /* first command parameter */
        UBYTE   io_Parm1;               /* second command parameter */
        UBYTE   io_Parm2;               /* third command parameter */
        UBYTE   io_Parm3;               /* fourth command parameter */
    };

See the include file exec/io.h for more information on iostdreq and the
include file devices/printer.h for more information on iodrpreq and
IOPrtCmdReq.

 opening the printer device 
 writing text to the printer device 
 important points about print requests 
 closing the printer device