Appendix A Data Compression
Data compression is done using a form of run length encoding. Bit seven, the sign bit, of
a compressed character represents the value to be printed: 0 = white space, 1 = printed
pixel. Bits 0 through 6 represent the number of consecutive bits of the selected value
minus one, as shown in the table below.
Compressed Data Byte Layout
Bit
7 6 5 4 3 2 1 0
Function
Pixel color (Number of pixels to print)-1
Value
White = 0
Black = 1
0..127
Examples:
00h = 1 white pixel
80h = 1 printed pixel
0Fh = 16 white pixels
FFh = 128 printed pixels
The data is handled by the printers on a line-by-line basis, so compressed lines
may be intermixed with normal lines. In addition, compressed mode also uses the
Bytes-per-Line variable to determine how much data to expect from the host for
each line. However, the sum of the pixels must be equal to the Bytes-per-Line
variable multiplied by 8. No error checking is done on the incoming data and
unexpected results will occur if the above caution is not observed.
Copyright © 2006, DYMO Corporation Page 21
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