DEC LA120/210 Emulation
Graphics
Graphics mode gives the user complete control over every dot position on the paper. Graphics may be printed with 132 dpi horizontal density and 72 dpi vertical density.
Each byte of graphics data represents a vertical column of six dots, with the LSB (least significant bit) corresponding to the top wire of the print head. Turning a bit on causes a dot to be printed. Graphics bytes are encoded in the characters '?' (hexidecimal 3F) through 'DEL' (hexidecimal 7F). The graphics encoded characters are offset by the value 3F, so the bit values corresponding to each wire of the print head are shown below:
wire 1 (top) | '@' | (40 hex - 3F hex = 1) |
wire 2 | 'A' | (41 hex) |
wire 3 | 'C' | (43 hex) |
wire 4 | 'G' | (47 hex) |
wire 5 | 'O' | (4F hex) |
wire 6 | '_' | (5F hex) |
The appropriate bit values are added together to fire the appropriate wires. For example, the character 'P' (50 hex - 3F hex = 11 hex) will fire the top wire, wire 1, and the fifth wire, wire 5.
Each graphics sequence contains any number of bytes followed by the terminating sequence ESC \ (hexadecimal 1B 5C).
Escape Sequence: | ESC | P | q | data | data ... ESC | \ | |
Hexadecimal: | 1B | 51 | 71 | (3F - 7F) | 1B | 5C | |
When printing graphics lines, the effective line pitch is 12 lpi. To make successive strips of a graphics image to align correctly, this lpi should be set prior to the carriage return after printing the first graphics line. The escape sequence ESC [ 3 z will accomplish this. Make sure to set the lpi back to your previous setting prior to the carriage return following the last line of graphics. For example, when printing text at 6 lpi and printing three lines of graphics:
ESC P q (data) ESC \ ESC [ 3 z (return) | prints graphics and does 1/12" line feed. |
ESC P q (data) ESC \ (return) | prints graphics and does 1/12" line feed. |
ESC P q (data) ESC \ ESC [ 0 z (return) | prints graphics and does 1/6" line feed. |
Note that graphics mode must be exited before issuing any escape sequence, or carriage returns and line feeds.
81
