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Grundlagen FlexRay BasicsV 1.1 20
2.5 Signal transmission
FlexRay uses two twisted wires for transmitting signal data. The transmission uses differential
voltage levels around 2.5V. The transmit level uBus results out of the difference between uBP
and uBM.
Figure 2.14 FlexRay level diagram [FREPLS06]
Using the different levels shown in Figure 2.14, the FlexRay bus can have four different
states:
• Idle_LP (Idle Low Power) – the level uBus is 0 V, and transceivers pull the voltage
level of the FlexRay bus to GND.
• Idle – the level uBus is 0 V, uBP and uBM are 2.5 V
• Data_0 – the level uBus is -2 V, since at least one FlexRay transceiver has set Bus
Plus to 1.5 V and Bus Minus to 3.5 V.
• Data_1 – the level uBus is -2 V, since at least one FlexRay transceiver has set Bus
Plus to 3.5 V and Bus Minus to 1.5 V.
The bus states Idle, Data_0 and Data_1 are detected by the Bus Drivers in normal mode of
operation, and have different values, depending on their position in the network. These Test
Points (TP) are defined in Figure 2.15, and Table 2.1 shows the valid levels of uBus.
Additionally, Figure 2.16 shows the timing of the falling and rising edges and the signal
duration.
Bäurle 12.10.2012