It is possible that if you have a basic program running in yourMVI56-BAS and you have the port 1 connected to a device thatperiodically send data, sometimes the basic program may be changed. This can happen if your device sends the ^c (Ctrl C) character (ASCII 03) to the BASIC module, changing the mode of the basic module to program,then the next received characters can be accepted as a new program line.
To avoid this you can use the call 19 (disable ^c checking) at thebeginning of your program.