HP 4 FAMILY - Manual (Page 135)

Comments:
MODE. Determines the interpretation mode as follows:
0 Interprets each byte as a character (8-bit mode
where the default row_number equals "0").
Computed character code is equal to
(row_number * 256) + 8-bit code sent in LB or SM
command.
1 Interprets the next two bytes as a character (16-bit
mode). LB and SM commands will read two bytes
to form one 2-byte character code equal to
(first_byte * 256) + second_byte. Label terminator
and 8-bit control codes must be preceded by a
NULL byte. To turn symbol mode off while in 16-bit
mode, you must send SM<NULL>; where NULL is
ASCII or decimal 0.
2 Same logic as mode 0, except that vertical
substitutes are used if found in a VT segment of
the current font. Characters are rotated counter
clock-wise to match the vertical-rotated printing
mode of the Character Text Path Direction
command. Default row_number equals "0".
3 Same input logic as mode 1, except that vertical
substitutes are used if found in a VT segment of
the current font. Full width characters are rotated
counter clock-wise to match the vertical-rotated
printing mode of the Character Text Path Direction
command.
Printer-Specific Differences 2-99