Bus messages
Bus messages |
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.
As in the 9-5, the Airbag and ABS control modules do not have a bus connection.
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 on the P-bus is ten times faster than on the I-bus. The reason for this is that the powertrain systems need information as quickly as possible 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.
The transmission of information between the control modules is achieved on two leads, bus+ (green lead) and bus- (white lead). The leads are twisted to increase tolerance to electrical interference.
The main unit uses the following information |
The main unit transmits the following information |