HP PCL/PJL reference (PCL 5 Printer Language) - Technical Reference Manual Part I

EN Character Descriptor Formats 11-69
Character Data Size (UI)
The value of the Character Data Size should equal the sum of the
sizes of the Character Data Size, Glyph ID, and TrueType Glyph Data
fields. This value alerts the PCL interpreter when a continuation block
is needed. The minimum possible value is 4. The value of Character
Data Size plus Descriptor Size plus 4 (for the Format, Continuation,
Reserved and Checksum bytes) will never be less than the value #
given in the character download command. If the sum is exactly equal
to #, then no continuation block is to be expected for the given
character. However, if the sum exceeds #, then a continuation block
is needed. A condition for the validity of a downloaded scalable
TrueType character is that the sum of the # values for all of that
character’s data blocks equals the sum of the Descriptor Size and
Character Data Size and 2 (for Reserved and Checksum), plus 2
times the number of character data blocks (for Format and
Continuation bytes).
Glyph ID (UI)
This field is used by the TrueType font scaler as an ID number for the
glyph data associated with the given character.
TrueType Glyph Data
This field contains the data segment associated with the given
character as found in the glyf table of the original TrueType font file.
See the description in True Type Font Files.
Checksum (UB)
The value of this byte, when added to the sum of all of the bytes in
the Character Data Size, Glyph ID, and TrueType Glyph Data fields,
should equal 0 in modulo 256 arithmetic. The Checksum is found only
in the last character data block associated with a given character.