Logitek Electronic Systems AE-32 Audio Engine - Manual (Page 16)

System Components
Logitek Audio Engine Reference Manual 14
Communication verification
You can verify communications between the Audio Engine and Control Surface, by noting the LCD
screen on the Audio Engine. The LCD screen should display
Rx= followed by a digit 1 to 4. This
digit indicates receipt of data on the specified Control Surface port.
When the Audio Engine receives information from the Supervisor PC, Rx=4 will be displayed.