B&B Electronics manual Message Transmission sending data to the 1939STB

Message Transmission (sending data to the 1939STB)

The transmission window is divided into three rows. The first row is the internal header information. The second row contains message control information. The third row is the data payload sent with the information.

The first row has 4 bytes. Bytes 1 and 2 are set to 8 and 21 hex. All data is entered in hex. The next two bytes, 3 and 4, are set by the user. Refer to pages 6 and 7 of this manual for help setting theses two bytes. Setting a byte is done by clicking in the box under the label and entering the proper hex value. All values in this row must contain information or the message will be rejected.

The second row contains bytes 5 though 11. These bytes are set by the user. All values are entered in hex. All of the bytes in this row do NOT have to contain data for the message to be accepted.

The last row is the data payload that is transmitted with an SAE-

J1939 message. This row may contain data or left blank.

Message Reception

To receive information from the SAE-J1939 bus, the user must program the 1939STB to receive a message. This is done by first sending a receive message to the 1939STB. Page 18 explains how to configure a message to receive data. After the proper byte codes are entered into the 1939STB, the device “listens” on the SAE-J1939 bus for a message that matches the identity code of the reception message. The message header information and data are displayed in the lower window. The incoming data will fill in the slots from top to bottom. Once the data moves off the page it is lost. If a permanent copy of the data is needed use “Data Logging”.

NOTE: MicroSoft Visual Basic only allows a buffer of approximately 3K. You must manually clear the Receive Message buffer or you will get a buffer overflow error.

34	1939STB4600 Manual
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