Explanation of communication report 01 and 07 for a READ_VAR or WRITE_VAR.

Issue
Explanation of communication report 01 and 07 that is returned when the Ethernet cable is removed..

Product Line
M340 CPU and BMXNOE01xx

Environment
Unity
Resolution
The following will explain the behavior on how a communication report 01 and 07 for a READ_VAR or WRITE_VAR is returned. The results are based upon a timeout value of 15 in the %MW+2 word of the function block management table.

After the cable is pulled, the NOE send out a retransmission followed by a few new queries. Any unanswered queries gets added to the memory buffer in the module. Five retransmissions (new queries are also sent out in between the retries) are sent out with the time difference between retries that is based upon an algorithm.. If the NOE does not get a response after the fifth retry, the communication report 01 is sent back. After sending out more new queries and not getting a response back, it sends another retry and returns communications report 01. It repeats this process for 6 more retries.

After a total of 12 retries, it resets and closes the connection. It then attempts to open a new connection. The 07 report is returned when the NOE does not get a response back on the attempt to open a new connection using a new port. It repeats the attempt to open a new connection using the same new port number. After trying for a while, it gives up and tries to open another new connection using a different new port number. When there is no response, it returns a communications report 07. This process is repeated.