Siemens ET 200SP Operating Instructions Manual page 51

● Monitoring time for S and U frames (t
Monitoring time for the acknowledgment of data frames of the master by the CP.
After receiving data from the master, the CP acknowledges the received data
alternatively:
– If the CP sends data to the master itself within t
– The CP sends an acknowledgment frame (S format) to the master at the latest when t
The value of t
● Idle time for test frames (t
Monitoring time during which the CP has not received any frames from the master.
When t
This parameter is intended for longer times without data traffic.
● Difference between send sequence number N(S) and receive sequence number N(R)
Maximum number of unacknowledged data frames (I-APDUs) as maximum difference
between send sequence number N(S) and receive sequence number N(R).
When k is reached and t
the frames sent have been acknowledged by the master.
When k is reached and t
● Max. number of unacknowledged data frames
Maximum number of received data frames (I-APDUs), after which the oldest frame
received from the master must be acknowledged.
Acknowledgment mechanism for the IEC protocol
With each sent data frame, the CP sends a continuous send sequence number. The data
frame remains initially stored in the send buffer.
When it receives the data frame, the master sends the send sequence number from this or
(if several frames are received) the last frame as an acknowledgement to the CP. The CP
saves the send sequence number returned by the master as a receive sequence number
and uses it as an acknowledgement.
Frames whose send sequence number is equal to or lower than the current receive
sequence number are evaluated as having been successfully transferred and are deleted
from the send buffer of the CP.
Recommendations of the specification:
● w should not be higher than 2/3 of k.
● Recommended value for k: 12
● Recommended value for w: 8
CP 1542SP-1, CP 1542SP-1 IRC, CP 1543SP-1
Operating Instructions, 01/2017, C79000-G8976-C426-03
received from the master during t
format).
elapses.
should be less than that of t
2
3
elapses, the CP sends a test/control frame (U format) to the master.
3
has not yet elapsed, the CP does not send any frames until all
1
has elapsed, the TCP connection is terminated.
1
4.5 Telecontrol communication (CP 1542SP-1 IRC)
)
2
at the same time along with the sent data frame (I
2
.
1
)
Configuration and operation
, it acknowledges the data frames
2
2
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