TSS461C datasheet(11/57 Pages) ATMEL

11 / 57 page

TSS461C

4193G–AUTO–12/04

VAN Protocol

Line Interface

There are three line inputs and one line output available on the TSS461C. The three

inputs are 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 TSS461C 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.

Consequently, the VAN protocol is a CSMA/CD (Carrier Sense Multiple Access/Colli-

sion Detection) protocol, allowing for continuous bitwise arbitration of the bus, and non-

destructive (for the higher priority message) collision detection.

Figure 4. 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 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

TSS461C Datasheet(PDF) 11 Page - ATMEL Corporation