COP685BC datasheet(29/57 Pages) NSC

29 / 57 page

Frame Formats (Continued)

Note: This device cannot send an overload frame as a result of not being

able to process all information. However, the device is able to recog-

nize an overload condition and join overload frames initiated by other

devices.

If no message is being transmitted, i.e., the bus is idle, the

bus is kept at the “recessive” level.

Figure 22 and Figure 23

give an overview of the various CAN frame formats.

DATA AND REMOTE FRAME

Data frames consist of seven bit fields and remote frames

consist of six different bit fields:

Start of Frame (SOF)

Arbitration field

Control field (IDE bit, R0 bit, and DLC field)

Data field (not in remote frame)

CRC field

ACK field

End of Frame (EOF)

A remote frame has no data field and is used for requesting

data from other (remote) CAN nodes.

Figure 24 shows the

format of a CAN data frame.

FRAME CODING

Remote and Data Frames are NRZ codes with bit-stuffing in

every bit field which holds computable information for the in-

terface, i.e., Start of Frame arbitration field, control field, data

field (if present) and CRC field.

Error and overload frames are NRZ coded without bit stuff-

ing.

BIT STUFFING

After five consecutive bits of the same value, a stuff bit of the

inverted value is inserted by the transmitter and deleted by

the receiver.

Destuffed Bit Stream

100000x

011111x

Stuffed Bit Stream

1000001x

0111110x

Note: x = {0,1}

DS012067-53

FIGURE 21. CAN Message Arbitration

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