Bus communication

Bus communication

•	Control module ACC (216)

•	Radio connector C (267c)

•	Control module airbag/SRS (331)

•	Radio (353)

•	CD changer (355)

•	Control module PSM (357Dk)

•	Control module Trionic (430)

•	Control module TCM (502)

•	Control module M2.10.3 (505)

•

MIU (540)

•

SID (541)

•	Control module (547)

•	Control module STC (565)

•	Control module Trionic OBDII (589)

•	Control module EDC 15 (595)

•	Control module auxiliary heater (597)

•	Diesel pump (598)

•	Control module DICE (628)

•	Control module TWICE (632)

P-bus and I-bus

A bus is a number of wires on which information is sent digitally and serially. Digital means that the voltage difference between two wires has only two values, about 0V or 5V. The information is coded so that different combinations of pulses with values 0V and 5V have different meanings.

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

Half of the control modules in the Saab 9-3 are connected to the bus.

The bus is divided into the P-bus (Powertrain Bus) and the I-bus (Instrument Bus). Both buses are connected to the main instrument unit (MIU). The buses are electrically isolated from each other.

The diagnostics instrument is not directly connected to the bus but communicates via DICE, which is connected to the I-bus, and therefore has access to all the control modules connected to the bus.

The P-bus has a data transfer rate ten times higher than that of the I-bus. This is because the P-bus requires information with the least possible delay.

All information sent out by a control module is available to all other control modules connected to the bus. The MIU ensures that the information that is available on one bus is also available on the other.

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

The information is transferred between control modules via two leads, bus+ (green lead) and bus- (white lead). The leads are twisted to reduce their sensitivity 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	Ignition switch. The main unit uses the +B information only as logic voltage.
Key correct	-	TWICE	Immobilization function. The main unit uses the information for the theft protection function of the audio system.
CD changer information	Current settings	CDC	Information on a CD and its location. The main unit sends the information over the bus as text information to the SID, which shows the current setting on the display.
Vehicle speed	km/h, mph	MIU	Rear left wheel speed (lead from ABS). The main unit uses the information for the “speed-dependent volume” function.
Steering wheel controls	Seek >>, Seek <<, Vol +, Vol -, NXT, SRC	SID	Button control module input. The main unit uses the information to control the function (perform the command) selected with the steering wheel controls.
Rheostat level	0-100%	SID	Rheostat control module input. 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	Rheostat control module input reduced internally by a fixed value. The main unit uses the information to control the brightness of the Night Panel on its front display.
Night Panel	ON/OFF	SID	Button. The main unit uses the information to switch the Night Panel function on/off. When switched on, the light intensity on the main unit front display is reduced.
Display lighting	0-100%	SID	Rheostat control module input or light sensor, highest value. The main unit uses the information to control the light intensity on the front display of the main unit.
Diagnostics communication		DICE/Diagnostic instrument	Control module should be live and the bus leads intact. 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
Time RDS	Hours, Minutes, Seconds	SID	RDS reception. SID uses the information to the time function (clock).
RDS Date	0-31	SID	RDS reception. SID uses the information to the time function (clock).
Month RDS	January - December	SID	RDS reception. SID uses the information to the time function (clock).
Sound	Sound information	SID	Button pressing on dashboard. SID uses the information to activate the type of sound requested from the main unit.
Text message	Text information	SID CDC	Audio display. SID uses the information to show the settings for the current source on the display.
CD changer control	Information for controlling the CD changer	CDC	Buttons on dashboard. The CD changer uses the information from the main unit to control the function selected on the CD changer.
Diagnostics communication	-	DICE/Diagnostic instrument	Control module should be live and the bus leads intact For further information on the bus, see Bus and Diagnostics Communication.