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SB9600 is a Motorola proprietary TLL communications protocol. It uses a pair of inverted signal lines, BUS+ and BUS-, along with a BUSY (and complementary /BUSY) signal, to communicate between various components inside a radio, or between a radio and its control head.

Radios known to use SB9600 for control include:

Phy Layer

SB9600 signal diagram from the XTL2500 detailed service manual

The physical layer of SB9600 consists of complementary data and control lines. BUS+ & BUS- are bidirectional data lines and are complements of each other. BUS+ is active low and is essentially a standard UART line. BUS- is simply the inverse of BUS+. BUSY & /BUSY are bidirectional control lines used to avoid data collision and ensure only one device on the SB9600 bus is transmitting data at any given time.