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5.1.3 Transmit Message Status Byte Definitions
Refer to the “Master Commands and Responses” document for exact bit definitions of the status
byte that accompanies the transmit acknowledgment.
5.1.3.1 Transmit message example
The user has set the AVT-718 to VPW mode.
The user wants to send the following OBD-II query:
68 6A F1 01 00
.
The user assembles and sends the following packet to the AVT-718:
05 68 6A F1 01 00
.
After the AVT-718 has transmitted the message onto the network, successfully, the user receives
the following at the host computer:
01 60
5.1.4 Receive message format
Messages received from the network are assembled into the original byte sequence. The received
CRC or checksum is calculated and checked to be equal to the CRC or checksum byte at the end
of the received message. The received status byte is updated and the entire packet is sent to the
host.
Depending on the mode of operation, the received CRC/checksum byte is discarded or preserved
according to command $52 $01 $xx. (In VPW and CAN mode the CRC/checksum byte is
always discarded.)
Some modes of operation enforce format checking rules to the received message (even if it was
transmitted by the AVT-718). The user should consult the appropriate specifications and related
documents for details on the format of messages in specific modes of operation.
Status of all such tests are indicated in the received status byte.
5.1.4.1 Received message time stamping
All modes of operation support received message time stamping. This function is enabled or
disabled by the user through the use of the 5x 08 command.
If time stamps are disabled (default setting), then the format of a received message is:
◊
Header byte(s); 1 to 3 bytes.
(Depending on the packet size, one of the alternate header formats may be used.)
◊
Received status byte; 1 byte.
◊
Message bytes ...
If time stamps are enabled, then the format of a received message is:
◊
Header byte(s); 1 to 3 bytes.
(Depending on the packet size, one of the alternate header formats may be used.)
◊
Time stamp; 4 bytes.
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