Intel 87C196CB, 8XC196NT user manual Message Frames, Effect of Masking on Message Identifiers

CAN SERIAL COMMUNICATIONS CONTROLLER

Table 7-5. Effect of Masking on Message Identifiers

Transmit message object ID	1 1 0 0 0 0 0 0 0 0 0
Mask (0 = don’t care; 1 = must match)	0 0 0 0 0 0 0 0 0 1 1
Received remote message object ID	0 0 1 1 1 1 1 1 1 0 0
Resulting message object ID	0 0 1 1 1 1 1 1 1 0 0

7.3.3Message Frames

A message object is contained within a message frame that adds control and error-detectionbits to the content of the message object. The frame for an extended message differs slightly from that for a standard message, but they contain similar information. A data frame contains a message object with data to be transmitted; a remote frame is a request for another node to transmit a data frame, so it contains no data.

Figure 7-3 illustrates standard and extended message frames. Table 7-6 and Table 7-7 describe their contents and summarize the minimum message lengths. Actual message lengths may differ because the CAN controller adds bits during transmission (see “Error Detection and Management Logic” on page 7-9). After each message frame, an intermission field consisting of three recessive

(1) bits separates messages. This intermission may be followed by a bus idle time.

Standard Frame											End of
											Frame
				Arbitration			Control		Data Field	CRC	Ack
				Field			Field			Field	F.
			S	11-bit	R	I				15-bit
			O				r	DLC
				Identifier	T	D			0–8 Bytes
			F							CRC
					R	E	0
Extended Frame											End of
											Frame
			Arbitration				Control		Data Field	CRC	Ack
			Field				Field			Field	F.
S	11 bit	S	I	18-bit	R					15-bit
O		R	D		T	r	r	DLC	0–8 Bytes
	Identifier			Identifier						CRC
F		R	E		R	1	0
											A2599-01

Figure 7-3. CAN Message Frames

7-7