HP PCL 5 Reference Manual page 334

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.
15-26 Raster Graphics
EN