B&B Electronics 1939STB manual Reception of Data, SAE-J1939 Bus, ID Byte

Reception of Data

The 1939STB sends data to the RS-232 port and onto the PC using a 16 byte format. The first byte of the message is 42hex. The next byte is the Function byte. The next field displays the SAE-J1939 header. If an internal message is received then this field is filled with zero. The receive message header is detailed below.

Table 36. Message Received from the SAE-J1939 Bus

	I	Func			J1939 Address							M							Data
	D												C
	4		09	C		80		00		40			1	41		42	43	44		45	46	47	48	F
	2												E											F
	4		28		0		00		00		00		0		A										A
2				0								0		A										A

Table 36 shows the receive message. The black line separates the two types of messages that the 1939STB produces. Each message is detailed separately below.

SAE-J1939 Bus

Referring to Table 36 this is a message received from the SAE-J1939 bus. The first byte (ID) is the start of frame byte and is fixed at 42hex. The next byte is a function code byte. This byte is broken into two nibbles and decoded as follows:

Table 37. Function

		Nibble 2				Nibble 1
Bit 7	Bit 6		Bit 5	Bit 4	Bit 3	Bit 2	Bit 1	Bit 0

The gray area shown in Table 36 is information that was not received from the bus, but is needed to track the message.

ID Byte

This is a start of a message and will always be 42Hex.

1939STB4600 Manual 29

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