Multiplayer
Multiplayer can refer to 4P-capable games like Kizuna Encounter - Super Tag Battle using the NEO-FTC1B board, or multi-system cable-linked games like League Bowling, Riding Hero and Thrash Rally.
The linkable cartridges had a dedicated HD6301 µC and used a 3.5mm stereo jack cable to communicate with each other.
Protocol
Data is transmitted by the HD6301 using its SCI module, a data frame is composed of a start bit, 8 data bits then a end bit. Transmitted data is NRZ encoded, data rate seemingly is 62,500 bauds.
MVS Multiplayer
MVS carts are fitted with two 3.5mm jack plugs to daisy chain up to 4 systems. Cabinet ID is setup by hard dips, as well as comm enabling.