1. Printing Graphics An introduction to capabilities of the HP Printer Control Language

2. Escape-sequences The PCL language employs some special sequences of ASCII control-codes, known as ‘escape’ sequences (since they begin with the code for the escape-key: 0x1B) The character-sequence ‘\e’ may be used to generate this special non-printable byte The punctuation-symbols, numerals, and alphabetic characters that follow specify a specific command to the HP laser printer

3. Printer Communication An application that wishes to do printing can create a textfile containing a mixture of document text and PCL commands This text file is then ‘submitted’ to the printer using a Linux command (e.g., ‘lpr’) The printer recognizes commands by the occurrence of an ‘escape’ code

4. Initilization Printer initialization command has format: ESC E Example: fprintf( prn, “\eE” ); // This statement writes the initialization // command to a file whose file-pointer is // the ‘prn’ variable

5. Dots-per-inch Setting print resolution for raster graphics is done with the following command: ESC * t # R Here the ‘#’ symbol denotes a numeric parameter that specifies the number of dots-per-inch (i.e., the pixel resolution) Possible choices are: 75, 100, 150, 300

6. Set the Cursor Position Set the cursor’s Y-coordinate: ESC * p # Y Set the cursor’s X-coordinate: ESC * p # X Example: If dots-per-inch equals 300, then fprintf( prn, “\e*p%dY\e*p%dX”, 150, 150 ); places the cursor a half-inch from margins

7. Set the Compression Mode Here is the command that specifies the type of raster data-compression used: ESC * b # M The possible numeric parameters are: –0: unencoded (no compression) –1: run-length encoding –2: tagged image file format (TIFF) –3: delta row compression

8. Enter Raster Graphics Mode The printer’s default mode is ‘text’ mode To switch into raster graphics mode, the following command is issued: ESC * r # A Here the ‘#’ symbol specifies the type of cursor-positioning that is used: –1 means use current cursor position –0 means use the printer’s left margin

9. Sending Raster Data Here is the command for sending raster graphics data to the printer: ESC * b # W Here the ‘#’ symbol stands for a numeric parameter that specifies the number of bytes of raster data that follows the ‘W’ Then the cursor moves to the next row

10. Leaving Raster Graphics Mode To exit from raster graphics mode, the following command is used: ESC * r B This command switches the printer back to its normal ‘text’ mode, and it is issued after the final row of raster graphics data is sent

11. End-of-Page The PCL language is ‘page oriented’, and once a page’s description is complete, the printer should eject that page The ‘form-feed’ command ‘\f’ can be sent to the printer to eject the completed page: fprintf( prn, “\f” );

12. Our ‘wavprint.cpp’ demo We have posted an application program that prints certain Waveform Audio files, using the printer’s PCL raster graphics commands So far it only works with 8-bit non-stereo data-format To avoid wasting paper and toner, it only prints the first page of the waveform