Initially sold for ¥180,000
The Yamaha PC1 piano player control is part of the YIS ecosystem but seems to be able to operate independently from the central processing unit PU1. It's able to record and replay piano playing through a piano drive unit (PL1). Multiple songs can be recorder, replay can be done step by step and everything can finally be saved on a 5 1/4 floppy disk.
Behind a flap on the right side of the front panel there are three additional sliders, to control volume, tempo and transposition. The PC1 seems to be able to only record data information, so the "volume" probably relates to the "velocity" of the notes played.
At the moment, no information could be found about the data interface (a "piano" connector and a couple of "control line" 8 pin connectors). An identical PC1F model was also available, named "F series control unit". With the advent of MIDI, this device evolved in the PPC line of piano controllers.