Tally Genicom Matrix Printer Code 93 Checksums for Full ASCII

7265 Programmer’s Manual 60

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 ne ed 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” th at 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 com bination as a lowercase “a”.

So far, this process is transparent both to routines sendi ng symbol strings to the printer and to

routines receiving decoded data from the reader. When ASCII c haracters are represented as

character combinations, however, the reader expects to see a c hecksum based on the values of

these combinations; this is the reason that the control cod es are assigned values in the Code 93-

character table. The following example illustrates the c alculation of the check digits for the

symbol Cat :