Brother HL-2170W - Manual (Page 114)

CHAPTER 2 PCL - 95
Data compression compresses the original image data word by word (16 bits).
The compressed data consists of both horizontal compression which uses 16 bit, 8 bit and 4 bit repeating
patterns within 1 word or 2 words of data and vertical compression which indicates how many times to repeat
the same data as in the previous line within 1 word of data.
 Non-compressed data
When the most significant bit in the first 2 bytes is 0, the printer goes into non-compression mode. The
following 11 bits then indicate the number of words of data, the least significant 4 bits are not used. After that,
the image data follows word by word.
15 14 4 3 0
0 data word count (11 bits) not used
data 1 (16 bits)
:
data n (16 bits)
 16 bit repeating compressed data
When the most significant 3 bits in the first 2 bytes are in the order 1, 0, 0, the remaining 13 bits indicate the
number of times to repeat 16 bit data. The following 2 bytes should be the 16 bit data to repeat.
15 14 13 12 0
1 0 0 number of repeats(13 bits)
data to repeat(16 bits)
 8 bit repeating compressed data
When the most significant 3 bits in the first 2 bytes are in the order 1, 1, 0, the following 5 bits indicate the
number of times to repeat 16 bit (two by 8 bits) data. The remaining 8 bits should be the 8 bit data to repeat.
15 14 13 12 8 7 0
1 1 0 number of repeats data to repeat(8 bits)
(5 bits)
 4 bit repeating compression data
When the most significant 3 bits in the first 2 bytes are in the order 1, 0, 1, the following 4 bits are the 4 bit data
to repeat. The remaining 9 bits indicate the number of times to repeat the 16 bit (4 by 4 bits) data.
15 14 13 12 9 8 0
1 0 1 data to repeat number or repeats(9 bits)
(4 bits)
 Vertical repeating compressed data
When the most significant 3 bits in the first 2 bytes are in the order 1, 1, 1, the remaining 13 bits indicate the
same data words as in the previous line.
15 14 13 12 0
1 1 1 the same data words as in the previous line (13 bits)
The printer cannot support the APT and HRC function in the 1200 dpi printing mode.