Tally Genicom Matrix Printer - Manual (Page 64)

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Copyright © 2004 TallyGenicom Chapter 3 ANSI Bar Codes
Code 93 Checksums for Full ASCII
You can send any of the 128 ASCII characters verbatim in a Code 93 symbol. You would not
need to worry about Code 93 control codes if you did not need to compute checksums.
The four control characters in the Code 93 character table do not correspond to any byte values
sent to the printer, but instead refer to “precedence codes” that the printer generates. If you send
the printer a lowercase “a” in a Code 93 symbol, for instance, then the printer prints bars and
spaces that correspond to the <CTRL> + code in front of bars and spaces that correspond to the
uppercase “A”. The reader then interprets this character combination as a lowercase “a”.
So far, this process is transparent both to routines sending symbol strings to the printer and to
routines receiving decoded data from the reader. When ASCII characters are represented as
character combinations, however, the reader expects to see a checksum based on the values of
these combinations; this is the reason that the control codes are assigned values in the Code 93-
character table. The following example illustrates the calculation of the check digits for the
symbol Cat :