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, ABS (547)
- Control module STC (565)
- Control module, Trionic OBDII (589)
- Control module EDC 15 (595)
- Control module, extra heater (597)
- Diesel pump (598)
- Control module, DICE (628)
- Control module, TWICE (632)

P Bus And I Bus:

A "bus" in this context means cables through which information is sent digitally and serially. By digital is meant that the voltage difference between the cables has only two values, approx. 0 and 5 V. The information is coded so that different combinations of pulses with the values 0 and 5 V denote different things.
By serial is meant that the information is sent in express packages" one after the other in very fast succession. In the Saab 9-3, half of the car's control modules are connected to the buses.
The buses consist of a P bus (Power-train 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 DICE, one of the control modules connected to the I bus, and has therefore access to all the control modules connected to the bus.
The data transfer rate on the P bus is ten times higher than the I bus. The reason for this is that the power-train systems cannot work properly unless information is transferred with the minimum possible delay.
All the information sent from one control module is accessible to all other control modules connected to 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.
Information is transferred between the control modules via two leads, BUS+ (green lead) and BUS- (white lead). The two leads are twisted together to reduce their sensitivity to electrical interference.