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S5-115F Manual
Special features of the message structure
The messages of a slave S5-115F PLC must have a special header. The message header is necessary
for protecting the message data and consists of a 16-bit signature, a destination slave protection
byte and a message change byte. The message header is always transmitted automatically by the
S5-115F before the net data.
The messages of a PLC of the S5-U range do not have the S5-115F message header. For this reason,
you must take note of the following when exchanging data between a slave S5-115F PLC and a
slave PLC of the S5-U range:
Sending a message from a slave PLC of the S5-U range to a slave S5-115F PLC
Messages are only accepted by the slave S5-115F PLC if the complete message header is written to
the Receive mailbox. The message header contains information to protect the message, such as
the length of the message sent, the destination slave number, signature and message change byte
( Tables 7-11 and 7-12).
To calculate the signature you would require special information which is beyond the scope of this
manual. If you want to send messages from a slave PLC of the S5-U range to a slave S5-115F PLC,
please consult your local Siemens regional office.
Safety note
•
Inclusion of the security information ensures the correct transmission path. The net
data sent is nonsafety-related data, since it comes from a nonsafety-related
programmable controller. If you want to use the net data transmitted for safety-
related processing, you must subject the data received to a validity check.
•
To ensure that a message received from a PLC of the S5-U range is not delivered to
the mailbox of a different partner if the destination address is corrupted, you must
choose a message length which is not used by any other node.
Sending a message from a slave S5-115F to a slave of the S5-U range
The PLC of the S5-U range receives the message header and the actual net data.
Evaluation of the message header is not necessary and is left to the user's discretion.
EWA 4NEB 811 6148-02
Communications Capabilities
7-29
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