The B8512G and B9512G have slots for two B430 Plug-in Telephone Communicators to provide redundant telephone connections.
Upon power up the panel uses the B430 in the Mod-1 slot until a Test Report is initiated or when the panel phone supervision declares the line currently in use as failed.
B430, B8512G, B9512G
How to force Remote Programming Software (RPS) to connect to the panel from a keypad.
Remote Programming Software, Answer, 2000 series, D2212, D2412, D2812, D4412, D6412