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128 Universal Control Commands
THREE CATEGORIES OF DATA BYTES
The printer takes specific action for each data byte received. Two types
of action are possible: A character is printed or a controlling operation is
performed. All data bytes are classified into three categories:
•
Printable characters
•
Control codes
•
Elements in a control sequence or command
Each category is described in the following paragraphs.
Printable Characters
Characters are printable symbols: Letters, numbers, punctuation marks,
graphic shapes, and all other symbols that can be printed as a unit within
a single cell. A blank space is also a valid character.
Control Codes
A control code is a single byte of control information that modifies printer
action. It commands the printer to change something. For example, a
control code sent to the printer might advance the paper to the top of the
next page or it might sound the beeper.
Control codes are assigned to data bytes according to the emulation
active in the printer. Specific assignments are shown in Appendix D. The
majority of the control codes are normally assigned to data bytes between
0 and 31 decimal and between 128 and 159 decimal.