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P-bus and I-bus

P-bus and I-bus

A bus is 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” one after the other in rapid succession.

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

Communication takes place ten times faster on the P-bus than on the I-bus. This is because the powertrain systems require information with the shortest 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 transfer of information between control modules takes place on two leads, bus+ (green cable) and bus- (white cable). Both bus leads are twisted to increase resistance to electrical interference.