Raymarine stand-alone master instrument - Manual (Page 13)

10 ST30 Bidata Operation and Installation Handbook
1.5 Connection to adjacent ST30 Instruments
The ST30 Bidata is supplied with a daisy-chain cable that allows adjacent
ST30 instruments to be linked together. The daisy-chain cable supplies
power to adjacent instruments and allows data to be transmitted and
received via the SeaTalk bus.
The daisy-chain cable plugs into one of the SeaTalk ports on the back
cover.