TSS461F datasheet(13/57 Pages) ATMEL

13 / 57 page

7615A–AUTO–02/06

TSS461F

Figure 7 shows a normal VAN bus frame. It is initiated with a Start of Frame (SOF) sequence

shown in Figure 9. The SOF can only be transmitted by an autonomous module. During the pre-

amble, the TSS461F will synchronize its bit rate clock to the data received.

Figure 9. Framing Sequences

When the complete SOF sequence has been transmitted or received, the circuit will start the

transmission or reception of the identifier field.

All data on the VAN bus, including the identifier and Frame Check Sum (FCS), are transmitted

using enhanced Manchester code.

In enhanced Manchester code, three NRZ bits are transmitted first followed by one Manchester

bit, then three more NRZ bits followed by one Manchester bit and so on.

Since the high state is recessive and the low state is dominant, the bus arbitration can be done.

If a module wants access to the bus, it must first listen to the bus during one full End of Frame

(EOF) and one full Inter Frame Spacing (IFS) period, to determine whether the bus is free or not

(i.e.,no dominant states received).

Figure 10. Data Encoding

The IFS is defined to be a minimum of 64 prescaled clocks periods. The TSS461F, accepts an

IFS of zero prescaled clocks for the reception only of a SOF sequence.

VAN BUS

SEQUENCE

VAN BUS

SEQUENCE

NUMBER OF

PRESCALED

CLOCKS

PREAMBLE

START OF FRAME

START

SYNC

END OF

DATA

ACK

END OF FRAME

112 128 144

160 176 192

VAN BUS

SEQUENCE

VAN BUS

SEQUENCE

VAN BUS

SEQUENCE

NUMBER OF

PRESCALED

CLOCKS

NRZ 0

NRZ 1

MANCHESTER 0

MANCHESTER 1

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