COP888EB datasheet(31/75 Pages) NSC

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Frame Formats (Continued)

ACK FIELD

The ACK field is two bits long and contains the ACK slot and

the ACK delimiter. The ACK slot is filled with a “recessive” bit

by the transmitter. This bit is overwritten with a “dominant” bit

by every receiver that has received a correct CRC se-

quence. The second bit of the ACK field is a “recessive” bit

called the acknowledge delimiter. As a consequence the ac-

knowledge flag of a valid frame is surrounded by two “reces-

sive” bits, the CRC-delimiter and the ACK delimiter.

EOF FIELD

The End of Frame Field closes a data and a remote frame. It

consists of seven “recessive” bits.

INTERFRAME SPACE

Data and remote frames are separate from every preceding

frame (data, remote, error and overload frames) by the inter-

frame space see

Figure 22 and Figure 23 for details. Error

and overload frames are not preceded by an interframe

space. They can be transmitted as soon as the condition oc-

curs. The interframe space consists of a minimum of three

bit fields depending on the error state of the node.

These bit fields are coded as follows:

The intermission has the fixed form of three “recessive” bits.

While this bit field is active, no node is allowed to start a

transmission of a data or a remote frame. The only action to

be taken is signaling an overload condition. This means that

an error in this bit field would be interpreted as an overload

condition. Suspend transmission has to be inserted by error-

passive nodes that were transmitter for the last message.

This bit field has the form of eight “recessive” bits. However,

it may be overwritten by a “dominant” start-bit from another

non error passive node which starts transmission. The bus

idle field consists of “recessive” bits. Its length is not speci-

fied and depends on the bus load.

DS012837-23

An error frame can start anywhere in the middle of a frame.

DS012837-24

INT = Intermission

Suspend Transmission is only for error passive nodes.

DS012837-25

An overload frame can only start at the end of a frame.

FIGURE 20. CAN Control Frames

DS012837-26

FIGURE 21. CAN Frame Format

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