HP 2100 M EN - Manual (Page 171)

EN Appendix D Printer Commands 159
Many printer commands use the lowercase letter l ( l ) and the number
one (1), or the uppercase letter O ( O ) and the number zero ( 0 ). These
characters may not appear on your screen as shown here. You must
use the exact character and case specified for PCL printer
commands.
The following illustration displays the elements of a typical printer
command (in this instance, a command for page orientation).
Escape character
(begins escape sequence)
Value field (contains both
alpha and numeric characters)
Category of command
Uppercase letter
(terminates escape sequence)