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DESIGN OF A CUSTOM ASIC INCORPORATING CAN™ AND 1 ...

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one of the first two bits of this field is dominant then it is assumed an Overload Frame<br />

has begun.<br />

The Extended Format Data Frame is nearly identical to the Standard Format Data Frame<br />

(Figure 3.3). The only differences between these two formats are found in the IDE bit in the<br />

Arbitration Field for an Extended Data Frame (in a Standard Data Frame the IDE bit resides in<br />

the Control Field), and the size and arrangement of the Arbitration Field. Both the Standard Data<br />

Frame Format and the Extended Data Frame Format can coexist in the same CAN system.<br />

The rule is that Standard Data Frames always have priority over the Extended Data Frames.<br />

Figure 3.4 shows the format for an Extended CAN Data Frame. The following is a description<br />

of the Arbitration and Control Fields:<br />

1 bit<br />

Start-Of-Frame<br />

11 bits<br />

Standard Message Identifier<br />

1 bit<br />

Substitute Remote Request<br />

Arbitration Field<br />

1 bit<br />

Identifier Extension<br />

18 bits<br />

Extended Message Identifier<br />

1 bit<br />

Remote Transmission Request<br />

1 bit<br />

r1<br />

1 bit<br />

r0<br />

Control<br />

Field<br />

4 bits<br />

Data Length Code<br />

51<br />

0 – 8 bytes<br />

Data Field<br />

15 bits<br />

CRC Sequence<br />

CRC Field<br />

1 bit<br />

Delimiter<br />

Acknowledgement Slot<br />

Figure 3.4 Extended CAN Data Frame Format [18].<br />

1 bit<br />

1 bit<br />

Delimiter<br />

ACK<br />

Field<br />

7 bits<br />

End-Of-Frame<br />

3 bits<br />

Interframe Space

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