TSS461C datasheet(13/57 Pages) ATMEL

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TSS461C

4193G–AUTO–12/04

Figure 6 shows a normal VAN bus frame. It is initiated with a Start of Frame (SOF)

sequence shown in Figure 8. The SOF can only be transmitted by an autonomous mod-

ule. During the preamble, the TSS461C will synchronize its bit rate clock to the data

received.

Figure 8. 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 9. Data Encoding

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

TSS461C Datasheet(PDF) 13 Page - ATMEL Corporation

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