TSS463B datasheet(14/59 Pages) ATMEL

14 / 59 page

TSS463B

4102E–AUTO–12/04

VAN Protocol

Line Interface

There are three line inputs and one line output available on the TSS463B. that of the

three inputs to use is either programmable by software or automatically selected by a

diagnosis system.

The diagnosis system continuously monitors the data received through the three inputs,

and compares it with each other and the selected bitrate. It then chooses the most reli-

able input according to the results.

The data on the line is encoded according to the VAN standard ISO/11519-3. This

means that the TSS463B is using a two level signal having a recessive (1) and a domi-

nant (0) state. Furthermore, due to the simple medium used, all data transmitted on the

bus is also received simultaneously.

The VAN protocol is hence 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 messa ge) collision detection.

Figure 10. CSMA/CD Arbritration

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 itself that 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 trans-

ceivers are not able to receive the signal that they transmit.

Node a: TxD

Node a loses the arbitration

Node a releases the bus

Node b wins the arbitration

Node c loses the arbitration

Node c releases the bus

Node b: TxD

Node c: TxD

On Bus: DATA

Arbitration field

R: Recessive Level

D: Dominant Level

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