Siemens SIMATIC TIM 3V-IE DNP3, System Manual

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Glossary
TIM DNP3
System Manual, 12/2015, C79000-G8976-C253-04
343
TD7onTIM does not support the general request.
Image memory / send buffer
A TIM has a send buffer and an image memory for buffering send messages.
The data of the process image of the CPU configured for transfer by the TIM in the objects of
the TD7onTIM is written continuously to the image memory of the TIM.
Before it is forwarded to the communications partner, each message is entered in the send
buffer. Once it has been sent, the message is cleared from the send buffer. The size of the
send buffer depends on the type of TIM.
A message is transferred either based on the send buffer principle or the image memory
principle. The type of transmission is specified during configuration of the objects (data
points) using the 'Event' attribute. See also 'Image memory principle' and 'Send buffer
principle'.
Image memory principle
A fixed position is reserved in the image memory for each data message transferred to the
TIM for transmission. Each newly transferred message always overwrites the old message in
the image memory. The image memory therefore contains all data messages with their up-
to-date content from the process.
If a send message is entered using the image memory principle, only a reference to the
location of the message in the message image memory is entered. If the TIM has not yet
been able to transmit the message when the same message is transferred to it again, the
message is not entered in the send buffer a second time, but rather the image is simply
updated.
At the time of transmission, the message is sent with its up-to-date content from the image
memory. Only then can the message be entered in the send buffer again.
Transmission using the image memory principle achieves the following:
● The transmission path has less load. Fewer messages are transferred.
● The send buffer of the TIM is used less. An image memory message is entered a
maximum of once in the send buffer.
See also Image memory / send buffer.
LTOP
Line Transformer with Overvoltage Protection
Copper dedicated lines are highly susceptible to electromagnetic interference. The coupling
of extraneous voltages can be inductive or capacitive, for example due to the effects of
lightning. Direct conductive coupling is also possible due to bad insulation.
The LTOP overvoltage protection modules limit extraneous voltage and overvoltage to a
non-critical level. The floating transformer also provides electrical isolation preventing
coupling of voltages into other cable sections. An LTOP protects persons and investment
and is therefore an indispensable safety element in private dedicated line networks.