thanks for the info! I realized this wouldn’t help to run in a flash cart because the port for the VHD is built into the cart. Don’t believe the port was built into any MSX?
Vhd interface is only vi card/cartridge. No MSX has that buildin. And there is more than physical port to connect to VHD player. There is also separate CPU (80C49) in the IF-C9D card to communicate with VHD player. So most propably in cartridge versions (e.g. Victor IF-7900) there is also separate CPU inside.