Siemens Simatic RTU303xC Series Operating Instructions Manual page 229

● w
Maximum number of received data frames (I-APDUs), after which the oldest received
data frame must be acknowledged.
Permitted range: 1 .. 65535
Default setting: 8
● k
Maximum number of unacknowledged data frames (I-APDUs)
If k is reached and t
data has been acknowledged by the master.
When k is reached and t
Permitted range: 1 .. 12
Default setting: 12
● Discard events as long as the time of day is invalid.
If the option is enabled the values of data points configured as an event will be discarded
until the time of day of the RTU is synchronized or set.
This may be the case, for example, during startup of the RTU.
Acknowledgment
Mechanism:
With each sent data frame, the RTU 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 data frames are received) the last data frame as an acknowledgment to the RTU.
The RTU saves the send sequence number returned by the master as a receive sequence
number and uses it as an acknowledgement.
Data 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 RTU.
Recommendations of the specification:
w should not be higher than 2/3 of k.
Recommended value for k: 12
Recommended value for w: 8
RTU303xC
Operating Instructions, 06/2019, C79000-G8976-C382-06
has not yet elapsed, the RTU does not send any data until all sent
1
has elapsed, the TCP connection is terminated.
1
Configuration (WBM)
4.23 Telecontrol
229