B&B Electronics Command Response Protocol HVD100A3 - Manual (Page 18)

14 HDV100A3 Command & Response Manual-1306cr
B&B Electronics -- 707 Dayton Rd. -- PO Box 1040 -- Ottawa, IL 61350
PH (815) 433-5100 -- FAX (815) 433-5104
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
Number Byte
Value
(hex) Byte Function
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