B&B Electronics HVD100A3 Transmitting Data to the J1708 Bus, Priority Byte Value, Binary Value

Transmitting Data to the J1708 Bus

The HDV100A3 supports standard J1708 commands of up to 21 bytes. Additionally the HDV100A3 can send messages up to 100 bytes to the J1708 bus. It is the responsibility of the sending software to check for “ignition off” before using the J1708 bus to send messages with more than 21 bytes to the bus. Failure to check for a “quiet bus” condition before transmitting a long message may cause erratic bus operation. The format to send information to the J1708 bus is shown below:

Byte	Byte	Byte Function
Number	Value
	(hex)
1	01	Start of frame
2	03	Number of control bytes
3	01	ID bytes 1= J1708
4	12	Function code 12 (hex) transmit to J1708 bus
5	02	Priority byte 00000010 set bit 0 to 7 see below
6	XX	Number of data bytes to follow (excludes checksum byte)
	YY	Data bytes up to 100 bytes
	CS	Checksum

Set the priority bit using the chart below.

Priority Byte Value	Binary Value	Hex Value
1	00000001	01
2	00000010	02
3	00000100	04
4	00001000	08
5	00010000	10
6	00100000	20
7	01000000	40
8	10000000	80

14	HDV100A3 Command & Response Manual-1306cr
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