Bus communication

Bus communication

•	Control module, ACC (216)

•	Radio connector C (267c)

•	Airbag/SRS control module (331)

•	Radio (353)

•	CD changer (355)

•	PSM control module (357Dk)

•	Control module, Trionic T7 (430b)

•	Transmission control module, TCM (502b)

•	MIU (540d)

•

SID (541)

•	Control module (ABS) 547

•	Control module STC (565)

•	Control module, Trionic T7 OBDII (589b)

•	Control module, DICE (628)

•	Control module, TWICE (632)

Bus communication, other petrol-engine variants

•	Control module, ACC (216)

•	Radio connector C (267c)

•	Airbag/SRS control module (331)

•	Radio (353)

•	CD changer (355)

•	PSM control module (357Dk)

•	Control module, Trionic T5 (430a)

•	Control module, TCM (502)

•	Control module M2.10.3 (505)

•	MIU (540b)

•

SID (541)

•	Control module (ABS) 547

•	Control module STC (565)

•	Control module, Trionic T5 OBDII (589a)

•	Control module, DICE (628)

•	Control module, TWICE (632)

Bus communication, diesel

•	Control module, ACC (216)

•	Radio connector C (267c)

•	Airbag/SRS control module (331)

•	Radio (353)

•	CD changer (355)

•	PSM control module (357Dk)

•	MIU (540c)

•

SID (541)

•	Control module (ABS) 547

•	Control module STC (565)

•	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” which are transmitted one after the other in rapid succession.

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.

Only diesel-engined cars and cars with Trionic T7 have a P bus. Other petrol-engined variants have the same engine management system and automatic transmission as the earlier 900 model (T5, M2.10.3 and TCM) and these have no bus connections.

As in the 9-5, the Airbag and ABS control modules have no bus connections.

The diagnostic tool is not connected direct 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 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 the information sent from one control module is accessible for all 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.

Transmission of information between control modules occurs on two leads, bus+ (green lead) and bus- (white lead). The leads are twisted to increase tolerance to electrical interference.

TWICE uses the following information for theft protection

Information	Values	Off	The value depends on the following sensor input, signal or function
SID buttons	Clear, Set, Trip Down, Trip Up, Night Panel	SID	Buttons. TWICE uses the information to disconnect the glass breakage sensor and tilt sensor. The “Night Panel” button is used for this when the key is removed from the ignition.
Soft top position	Up/In motion/Down	STC	Switches on top of windscreen frame, Soft top cover switch. TWICE sends information to automatically disconnect the glass breakage sensor when the top is down and to allow opening the luggage compartment.
Identification number		MIU	Value created in MIU when immobilizer code is programmed in TWICE. TWICE uses the information for the immobilizer function.
Diagnostics communication		DICE/diagnostic tool	Control module should be powered and the bus leads intact See Bus and diagnostics communication

TWICE sends the following information for theft protection

Information	Values	Used by	The value depends on the following sensor input, signal or function
Immobilizer	ON/OFF	MIU (Cars with B204)	Immobilizer function. MIU uses the information to allow the engine to start. EDC 15 uses the information to allow the engine to be started.
Text message		SID	Anti-theft alarm function and central locking system function SID uses the information to show the text message for the theft protection.
Key correct	ON/OFF	Audio CDC	Immobilizer function. The audio system and CD changer use the information for the audio system theft protection.
Hazard flashers	ON/OFF	DICE	Anti-theft alarm function and central locking system function DICE uses the information to activate the hazard flashers when the alarm is activated.
Diagnostics		DICE/diagnostic tool	Control module should be live and the bus leads intact. See Bus and diagnostics communication