HP PCL/PJL reference - PCL 5 Comparison Guide

2-94 Printer-Specific Differences ENWW
The command byte itself has three parts:
• Control Bit. Determines whether the replacement data is
compressed, and also the bit boundaries of the command
byte's other two fields.
• Offset Count. The left offset (number of bytes) the
replacement data is offset from the current byte position in the
seed row.
• Replacement Count. The number of consecutive bytes to be
replaced. One more byte than the replacement count is
replaced (for example, 6 bytes are replaced by a replacement
count of 5).
Like compression method 3, the “current” byte follows the last
replacement byte; at the beginning of a row, the current byte
immediately follows left raster margin. An offset of 0 indicates the
current byte; an offset of 1 indicates the byte following the current
byte.
The size of the offset count and replacement count fields depends on
the value of the control bit.
CONTROL BIT = 0
If the control bit is 0, the replacement data is uncompressed. If the
control bit is 0, bits 0-2 indicate the replacement count and bits 3-6
indicate the offset count.
If the offset count is 15, an additional offset count byte follows and is
added to the total offset count. If the offset count byte is 255, another
offset count byte follows. The last offset count byte is indicated by a
value less than 255.
If the replacement count is 7, an additional replacement count byte
follows and is added to the total replacement count. If the
replacement count byte is 255, another replacement count byte
follows. The last replacement count byte is indicated by a value less
than 255. One more than the total replacement byte count will be
replaced.
Control Bit Offset Count Replacement Count
76 32 0
Control Bit = 0 Offset Count Replacement Count