Printronix MVP Series User Manual page 149

Invalid Control Code Sequence
An invalid control code sequence in the data steam will be treated as normal
ASCII characters. Printable characters will be printed and control characters
will be processed according to existing configuration options.
For example:
If CHR$ (4) or CHR$ (5) are used as headers and Configuration Options
24.1 or 25.1 have not been selected (default values 34.0 and 35.0 are in
effect), the line will be plotted as dot patterns rather than printed as
characters. Additional headers can be defined using Configuration
Options 31–33 and 36–41.
Programming 7–25