Bus communication

Bus communication

•	Trionic, engine management system (TRIONIC)

•	TCM (Transmission Control Module), control module for automatic transmission (502)

•	P-bus (Powertrain bus)

•	MIU (Main Instrument Unit) (540)

•	I-bus (Instrument bus)

•	SID (Saab Information Display) (541)

•	TWICE (Theft Warning Integrated Central Electronics) (632)

•	ACC (Automatic Climate Control) (216)

•	Audio, main unit (353)

•	CDC (CD Changer) (355)

•	PSM (Power Seat Memory) (357Dk)

•	PMM (Power Mirror Memory) (611)

•	DICE (Dashboard Integrated Central Electronics) (628)

•	Data link connector (H16-5/445)

•	Airbag (SRS) (331)

•	ABS (Anti Block System) (547)/TC-ABS (382)

P-bus and I-bus

A bus is understood to be the leads over which information is sent digitally and serially. Digital means that the voltage difference between the leads has only two values, roughly 0 V and 5 V. The information is coded so that different combinations of 0 V and 5 V pulses have different meanings.

Serial means that the information is sent in ”packets” which are transmitted one after the other in rapid succession.

All the control modules in the Saab 9-5 are connected to the bus, with the exception of those for the ABS and SRS.

The buses consist of a P-bus (Powertrain Bus) and an I-bus (Instrument Bus). Both buses are connected to the MIU (Main Instrument Unit). The buses are electrically isolated from each other.

The diagnostic tool is not connected directly to the bus but communicates via the DICE, one of the control modules connected to the I-bus, and so has access to all control modules connected to the bus.

The data transfer rate of the P-bus is ten times faster than that of the I-bus. The reason for this is that the powertrain systems need information with the least possible delay, as for example when providing air mass compensation when the selector lever is moved from N to D or torque limitation in connection with gear changing.

All the information sent from one control module is accessible to all the other control modules on the bus. The MIU is responsible for ensuring that information available on one bus is also available on the other bus.

The control modules send out information on the bus at regular intervals. The time between two transmissions depends on the information being sent and varies between 10 milliseconds (0.010 seconds) and 1 second. Information is also sent out by the control modules whenever the information changes.

The transfer of information between control modules takes place on two leads, bus+ (green lead) and bus- (white lead). The leads are twisted to reduce susceptibility to electrical interference.

The main unit uses the following information

Information	Values	From	The value depends on the following sensor input, signal or function
Ignition +B	ON/OFF	DICE	The main unit uses the +B information only as logic voltage.
Key Correct	-	TWICE	The main unit uses the information for the theft protection function of the audio system.
CD changer information	Current settings	CDC	Information on current CD and its location.
Vehicle speed	kph, mph	MIU	The main unit uses the information for the “speed-dependent volume” function.
Steering wheel switches	Seek >>, Seek <<, Vol +, Vol -, NXT, SRC	SID	The main unit uses the information to control the function (execute the command) selected via the steering wheel switches.
Rheostat level	0-100%	SID	The main unit uses the information to control the light intensity on the front display of the main unit.
Rheostat Night Panel	0-100%	SID	The main unit uses the information to control Night Panel brightness of the front lighting on the main unit.
Night Panel	ON/OFF	SID	The main unit uses the information to switch the “Night Panel” function on and off. When switched on, the light intensity on the main unit front display is reduced.
Display lighting	0-100%	SID	The main unit uses the information to control the light intensity on the front display of the main unit.
Diagnostics communication		DICE	For further information on the bus, see Bus and Diagnostics Communication.

The main unit transmits the following information

Information	Values	Used by	The value depends on the following sensor input, signal or function
RDS time	Hours, minutes, seconds	SID	SID uses the information for the time function (the clock).
RDS date	0-31	SID	SID uses the information for the time function (the clock).
RDS month	January - December	SID	SID uses the information for the time function (the clock).
Sound	Sound information	SID	SID uses the information to activate the type of sound requested from the main unit.
Text message	Text information	SID	SID uses the information to show on the display the setting of the source currently in use.
CD changer control	Information for controlling the CD changer	CDC	The CD changer uses the information from the main unit to control the function selected on the CD changer.
Diagnostics communication	-	DICE	For further information on the bus, see Bus and Diagnostics Communication.