Siemens Simatic S7-300 CP 341 - Figure 2-8 Data Traffic in the Event of an Initialization Conflict

Basic Principles of Serial Data Transmission
2.4 Data Transmission with the 3964(R) Procedure
CP 341 Point-to-Point Communication, Installation and Parameter Assignment
Manual, 09/2008, A5E02191071-01 45
Initialization conflict
The figure below illustrates the data transmission sequence during an initialization conflict.
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Figure 2-8 Data traffic in the event of an initialization conflict
If a device responds to the communication partner's send request (STX) within the
acknowledgment delay time by sending the STX character instead of the DLE or NAK
acknowledgment, an initialization conflict occurs. Both devices want to execute a pending
send request. The device with the lower priority withdraws its send request and responds
with the DLE character. The device with the higher priority sends its data in the manner
described above. Once the connection has been released, the lower-priority device can
execute its send request.
In order to resolve initialization conflicts you must assign different priorities for the
communication partners.
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