HP PCL/PJL reference (PCL 5 Color) - Technical Reference Manual

6-30 Raster Graphics EN
For command byte values 0 - 3, the two <# of bytes/rows> bytes
specify the number of bytes (row length) for the row. For command
byte values 4 and 5, these bytes identify the number of empty or
duplicate rows to print. The maximum value for these two bytes is
65,535; however, the image is clipped to the logical page. Thus, the
value of these bytes should not exceed the maximum number of
bytes/rows that can be printed on the current logical page size.
If an out-of-range command byte is encountered, the remainder of the
block is skipped, the cursor is not updated, and the seed row is
cleared.
Compression methods 0 - 3 are the compression methods used by
the Set Compression Method command. Value fields 4 and 5 are
features for the adaptive compression method and are explained
below.
Empty Row
A command byte of 4, empty row, causes a row of zero’s to be
printed. The number of rows printed depends on the value contained
in the two <# of bytes/rows> bytes following the command byte. The
empty row operation resets the seed row to zero and updates the
cursor position.
Duplicate Row
A command byte of 5, duplicate row, causes the previous row to be
printed again. The row can be duplicated the number of times
indicated by the value contained in the <# of bytes/row> byte.
Duplicate Row updates the cursor position but does not change the
seed row.