6
MOST Bus Diagnosis
Optical Bus
The MOST bus is a plastic optical waveguide. The MOST bus is coded in green in the E65
(Repair cables are black in color). The light wavelength is 650 nm (red light). The MOST
bus requires the following converter components:
Optical transmitter
Optical receiver
Each control unit of the MOST framework contains a transmitter and a receiver. The trans-
mitter and receiver have been developed by BMW. The low closed circuit (rest) current
properties of the transmitter and receiver enable optical wake-up by the MOST bus.
Optical Transmitter
A driver is fitted in the transmitter. The
driver energizes an LED (light-emitting
diode).
The LED transmits light signals on the
MOST bus (650 nm light, i.e. red visible
light). The repeat frequency is 44.1
MHz.
The sensing frequency on a CD player and for audio is 44.1 MHz; this means than no addi-
tional buffer is required, yet another reason why this bus system is so efficient for multi-
media.
Optical Receiver
The receiver receives the data from the
MOST bus. The receiver consists of:
An LED
A pre-amplifier
A wake-up circuit
An interface that converts the optical signal into an electrical signal
The receiver contains a diode that converts the optical signal into an electrical signal. This
signal is amplified and further processed at the MOST network interface.
Transmitter
Light LED Driver
Receiver
Light
LED
Pre-
Amp. Wake
-up
43-07-31
43-07-30
