Brother  HL-4140CN, Technical Reference Manual

Page: 111 / 517

CHAPTER 2 PCL - 92
If bit 6 and bit 5 are '1', then an optional offset byte follows the control byte. If the value of this optional
offset byte is 255, another (second) optional offset byte follows the first optional offset byte. The addition of
the offset count in the control byte and any optional offset bytes gives the total offset count.
If bits 4 to 0 are all '1', an optional replacement count byte follows the control byte or any optional offset
byte(s). If the first optional replacement count byte has a value of 255, a second optional replacement count
byte follows the first optional replacement count byte. Optional replacement count bytes will continue until
the value becomes less than 255.
<Example>
Seed row
55 55 55 55 55 55 55 55 55 55 55 55 55
Current row 55 55 55 11 11 11 55 55 66 66 66 66 55
<First section 11 11 11>
Offset count = 3
Replacement count = 3
Replacement data = 11
<Second section 66 66 66 66>
Offset count = 2
Replacement count = 4
Replacement data = 66
1 1 1 0 0 0 0 1
7 6 5 4 3 2 1 0
Replacement count = 1 + 2 = 3
Offset count = 3
Optional offset count byte = 0 Replacement data = 11
1 1 0 0 0 1 0
7 6 5 4 3 2 1 0
Replacement count = 2 + 2 = 4
Offset count = 2
Replacement data = 66 0
 # = 1152 indicates that CCITT G3/G4 data compression is to be used.
This format is popular in optical document storage areas as this compression is effective to store black and
white type pictures. As G3/G4 format does not have picture size/resolution information, the printer requires
a header at the beginning of the picture data. The header size is 94 Bytes. Both the header and the picture
data are transferred by the ESC*b###W(###=data length) command. The normal PCL transfer graphics data
command has a limitation on the data size and ### should not exceed 32767. Unlike other modes, this
mode is special and does not have the 32767 size limitation. The data must have the following structure -
Header and Picture data. The values in this mode are little endians.
Header
Picture data
94 bytes
Picture
data
length
File Length