Practical Industrial Data Networks:Design, Installation and ...

128 Practical Industrial Data Networks: Design, Installation and TroubleshootingNote that to transmit the data value of 10H, the sequence of data symbols DLE must beused. Only one of these DLE bytes and no embedded responses are included in the CRCvalue.Message limitationsT• Minimum size of a valid message is six bytes.• Duplicate message detection algorithm – receiver compares the second,third, fifth and sixth bytes of a message with the same bytes in the previousmessage.Re-transmit Same MessageDLESTX Data DLE EXT CRCMSG PacketTime Out LoopReceivedDLE ACK?YesNoReceivedDLE NAK?YesNoTimed Out?YesNoT3* NAKSReceived for thisMessage?YesPYes3* Timeoutsfor this Message?NoNoDLEENQFigure 9.2Software logic for transmitterP = Recovery procedureT = Ready to transmit next message* = Default values used by moduleDepending on the highway traffic and saturation level, there may be a wait for a replyfrom the remote node before transmitting the next message.