HP PCL 5 Comparison Manual page 136

Row Number. Used only in modes 0 and 2 (8-bit
modes) when a 16-bit character set is selected. The row
number indicates the first byte while the LB or SM
instruction will supply the second byte.
For example, if you send LMO,37, and you have selected
a 16-bit character set, sending LBAB<TERM> would
result in the device printing characters 65 and 66 from
row 37 of the character set grid.
If you are using an 8-bit character set in 16-bit mode
(modes 1 or 3), you must specify the first byte of each
character as 0. All other first byte calues are treated as
undefined characters.
Notes:
When LM switches modes, it turns off symbol mode
(executes SM;).
LM affects the way SM and LB interpret bytes.
LM does not affect the DT or DL commands.
DT allows 8-bit terminator definitions only. To terminate
a label in 16-bit mode, precede the current label termina-
tor by the null character (decimal 0). The only exception
is the ?E (Reset) instruction in dual-context devices. ?E
is executed regardless of the byte boundaries within LB
and SM.
2-100 Printer-Specific Differences