SummaryThe left port implements the Kempston ( IN (31) ) protocol. The right port implements the Sinclair Port #1 protocol (keys 6,7,8,9,0) but there is a known error that UP/DOWN (keys 8 & 9) are reversed from the Sinclair standard.
Remarksseparate programmable/dual-port types
DK'Tronics Dual Port Joystick Interface | ZXDB Entry