B&B Electronics 1939STB manual External Commands, J1939 Format

External Commands

The SAE-J1939 format is based on the CAN extended data frame. A detailed breakdown of the data frame is shown in Appendix A.

The arbitration field is changed to conform to the SAE-J1939 message frame. The message frame must be broken down further before it can be sent to the 1939STB.

The format for transmitting data to the 1939STB is shown in the following table:

Table 18. J1939 Format

Message Header				Message Information											Data Payload
B	B	B	B		B	B	B	B	B	B	B	B	B	B		B	B	B	B	B
1	2	3	4		5	6	7	8	9	1	1	1	1	1		1	1	1	1	2
										0	1	2	3	4		5	6	8	9	0
8	2	1	0		9	E	0	8	0	4	8	4	4	4		4	4	4	4	4
1	1	F	5		5	7	c	0	0	0	c	1	2	3		4	5	6	7	8

The message sent to the converter is formatted as shown above. The format is divided into three sections. Each section performs a specific function as follows:

Bytes 1 through 4 (B1-B4) are internal commands for the converter. These bytes tell the converter if the following message is intended for the SAE-J1939 bus, the slot where the message should be stored on the 1939STB, and the length of the data payload.

Bytes 5 through 11 are for message control - if it is to be transmitted (data frame) or received (remote frame). This area contains the J1939 message information: priority, data page, PDU format, PDU specific, and source address. The last section is the data section. This is the data that will be sent to, or received from, the bus. It may contain 0 to 8 bytes.

1939STB4600 Manual 13

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