B&B Electronics 1939STB manual Communication directed to the device Format

Communication directed to the device

Format:

Table 1. J1939STB Format

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

All communications to the device start with a message header (white

area). This header is removed from any message sent to the J1939 bus. The header is four bytes long. Two bytes (B1& B2) are used to confirm start of frame. The next two bytes (B3 & B4) contain information controlling how the 1939STB functions. The remainder of the packet is the data payload and can contain from zero to sixteen bytes depending on function.

Table 2. Transmit Data Format

Byte 1	Byte 2	Byte 3	Byte 4	Message Information	Data Payload
Check	Check	Control	Control
1	2	1	2

The first two bytes (Check 1 and Check 2) are always set to 81hex and 21hex. These bytes must precede all data sent to the device. If the Check bytes are not sent consecutively the message will be rejected. The entire message must be resent before data can be transmitted to the device. Control (byte 3 and byte 4) contain information that is used by the converter. This information is not passed to the J1939 bus. Both control bytes must contain data (cannot have a value of 00) or the transmission will be rejected.

1939STB4600 Manual 5

B&B Electronics Mfg Co Inc – 707 Dayton Rd - PO Box 1040 - Ottawa IL 61350 - Ph 815-433-5100 - Fax 815-433-5104

B&B Electronics Ltd – Westlink Commercial Park – Oranmore, Galway, Ireland – Ph +353 91 792444 – Fax +353 91 792445