E65/E66 K-Can
E65 K-CAN
Introduction
For the E65/E66, the functions that were incorporated within the main bodyshell electrical system on the E38 have been distributed among a number of separate control units. Those control units and various new control units are connected to the K-CAN.
The K-CAN is a new development and is subdivided into two sections, the K-CAN System and the K-CAN Peripherals.
Examples of new control units and functions on the K-CAN are the Car Access System (CAS),the Centre Console Control Center module (BZM),the Rear Centre Console Control Center module (BZMF) and the Power Module (PM).
K-CAN System/Peripherals
The subdivision of the K-CAN into the sections "SYSTEM" and "PERIPHERALS" relieves the load on the bus because the number of vehicle components (control units/modules) is divided between two "independent" bus systems.
Advantages of two K-CAN Busses
- In a crash, it is possible that components could fail as a result of a short circuit on the K-CAN. The K-CAN Peripherals covers such at-risk areas. If the K-CAN Peripherals were to fail, the K-CAN System would still remain functional.
- Addition of new vehicle components to either bus is possible at any time.(Maximum 40 control units per bus)
- Low data load on the bus system from bus users due to division into two sections.
- Greater reliability.
Voltage Level on the K-CAN.
If the CAN High voltage level changes from low to high, this represents a logical 1. If the voltage level changes back to low, this represents a logical 0. The voltage level on the CAN is in the range of 1V to 5V
NOTE: The voltage can alter as a result of a defective terminal resistor, for example. This has an effect on the CAN system. Communication between bus nodes no longer functions properly.
Terminal Resistor
An electrical conductor through which current passes always has an ohmic, an inductive and a capacitive impedance. When data is transmitted from point "A" to point "B" over a CAN line, the total sum of that impedance has an effect on the transmission of that data.
The higher the transmission frequency, the greater the effect of the inductive and capacitive impedance. The result of this can be that when the signal reaches the end of the data transmission line, it is unidentifiable. For that reason, the data line is "modified" by terminal resistors so as to preserve the original signal.
The inductive impedance is produced by phenomena such as the coil effect of the wire. The capacitive impedance for example is produced by the effect of routing the wire parallel to the vehicle body. The terminal resistors on a bus system vary. They are generally dependent on the following parameters:
- Frequency of data transmission on the bus system
- Inductive/Capacitive load on the transmission channel.
- Length of the data transmission cable (The longer the cable is, the greater is the inductive component).
The control units are categorized either as basic control units or other control units. Categorization is performed on the basis of the impedance level. Basic control units are those which always have to be fitted in the car regardless of equipment level or market. Other control units are those that are dependent on the options fitted.
The terminal resistor values for the K-CAN system are 820 Ohm for "Basic" controllers and 12K Ohms for all other control units.
For the E65/E66 the Basic controllers are:
K-CAN S:LM, IHKA, CAS, CD, ZGM, KOMBI.
K-CAN P: CAS, TMFAT, TMBFT, HKL
The resistors are located inside of the control units.
Wake-Up on the K-CAN
The control units on the K-CAN network are "awakened" via the bus. For that reason, it has been possible to dispense with the previous function of terminal 15 as wake-up line. The wake-up message is passed directly to the control unit output stage by the CAS module receiver. The output stage switches terminal 30 on and the unit is woken up.