TSS461 ATMEL Corporation, TSS461 Datasheet - Page 11

• Manufacturer Part Number: TSS461
• Description: VAN Data Link Controller
• Manufacturer: ATMEL Corporation

VAN Protocol
Line Interface
4194C–AUTO–01/06
There are three line inputs and one line output available on the TSS461E. Each of the three
inputs to use is either programmed by software or automatically selected by a diagnosis system.
The diagnosis system continuously monitors the data received through the three inputs, and
compares them and the selected bitrate. It then chooses the most reliable input according to the
results.
The data on the line is encoded according to the VAN standard ISO/11519-3. This means that
the TSS461E is using a two-level signal having a recessive (1) and a dominant (0) state. Fur-
thermore, due to the simple medium used, all data transmitted on the bus is also received
simultaneously.
Consequently, the VAN protocol is a CSMA/CD (Carrier Sense Multiple Access/Collision Detec-
tion) protocol, allowing for continuous bitwise arbitration of the bus, and non-destructive (for the
higher priority message) collision detection.
Figure 5. CSMA/CD Arbitration
In addition to the VAN specification there is also a pulsed coding of the dominant and recessive
states. This mode is intended to be used with an optical or radio link. In this mode, the dominant
state for the transmitter is a low pulse, (2x prescaled clocks at the beginning of the bit) and the
recessive state is just a high level.
When receiving in this mode, it is not the state of the signal which is decoded, but the edges.
Also, reception is imposed on the RxD0 input, and the diagnosis system does not operate
correctly.
In addition, in this mode there is an internal loopback in the circuit since optical transceivers are
not able to receive the signal that they transmit.
On Bus: DATA
Node a: TxD
Node b: TxD
Node c: TxD
R
D
R
D
R
D
R
D
R: Recessive level
D: Dominant level
Arbitration field
1
2
Node c loses the arbitration
Node c releases the bus
3
Node a loses the arbitration
Node a releases the bus
Node b wins the arbitration
TSS461E
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