Dymo LabelWriter 450 Duo Label Printer User Manual download pdf (Page 21)

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.

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Dymo LabelWriter 450 Duo Label Printer User Manual Page 21