SB9600

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:

• MTS2000 and MCS2000
• Astro Spectra
• All Astro25 radios

Physical Layer

SB9600 signal diagram from the XTL2500 detailed service manual. Note that this diagram incorrectly shows the BUSY signal as active high. The original SB9600 specification document calls for BUSY to be active low and /BUSY (not present on the XTL2500) to be active high

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.

SB9600 Signal Lines

Name	Description	Default State
BUS-	Bidirectional differential data bus, active high	Low (0V)
BUS+	Bidirectional differential data bus, active low	High (5V)
/BUSY	Bidirectional busy indicator, active high. Used for collision avoidance.	Low (0V)
BUSY	Bidirectional busy indicator, active low. Used for collision avoidance	High (5V)