On the KETRON products, there is a unique PIANIST feature (AUTO/SUSTAIN) where once you connect a SUSTAIN pedal to the SUSTAIN jack at the back of the Arranger unit, play a chord and press the pedal, any other subsequent notes/chords played are ignored (allowing you to 'solo' freely across the entire keyboard with no impact to the arranger/style). Once you release the pedal, the arranger now 'reads' chords played anywhere on the keyboard. This feature allows you to play like a PIANIST who generally sustains when playing notes aligned to the current chord played, and then releases the sustain pedal when about to play the next chord/notes
Hope this clarifies this.
Thanks,
PS:- On the 'newer' units like SD40, SD9 ... etc, sustain pedals polarity switch can be set, allowing you to use various types of sustain pedals from other manufacturers other than KETRON!