HP PCL/PJL reference - PCL 5 Comparison Guide

ENWW Printer-Specific Differences 2-95
CONTROL BIT = 1
If the control bit is 1, the replacement data is run length encoded. the
bit boundaries are different than if the control bit is 0: bits 5-6 contain
the offset count, and bits 0-4 contain the replacement count. As when
the control bit is 0, optional offset bytes and replacement bytes may
be added.
76 54 0
Control Bit = 1 Offset Count Replacement Count