B&B Electronics RS-232 to J1939 Converter CE 1939STB - Manual (Page 31)

1939STB4600 Manual 29
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B&B Electronics Ltd – Westlink Commercial Park – Oranmore, Galway, Ireland – Ph +353 91 792444 – Fax +353 91 792445
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
D
Func J1939 Address M
C Data
4
2 09 C 80 00 40 1
E
41 42 43 44 45 46 47 48 F
F
4
2 28 0
0
00 00 00 0
0
A
A 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:
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.
Table 37. Function
Nibble 2 Nibble 1
Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0