Siemens SIMATIC S7-300 Hardware And Installation Manual page 193

You can set any intelligent slave interrupts using SFB75
Applies to the following
CPUs
CPU 313C-2 DP
CPU 314C-2 DP
CPU 315-2 DP
SFB 75 "SALRM" is used to send a process or diagnostic interrupt from a slot in
the transfer area (virtual slot) to the associated DP master from the user program
on an intelligent slave. This starts the associated OB on the DP master.
Interrupt-specific additional information may be sent at the same time. You can
read all this additional information in the DP master using SFB 54 "RALRM".
Interrupts with another DP master
When CPU 31x-2 operates with another DP master, an image of these interrupts is
created in the device-specific diagnostic data of CPU 31x-2. You must post-
process the relevant diagnostic events in the DP master's user program.
Note
Before you can evaluate diagnostic and process interrupts using the device-
specific diagnostics function on another DP master, you must make sure that:
The DP master is able to store the diagnostic messages, i.e. the diagnostic
messages should be stored in a ring buffer on the DP master. For example, if the
DP master can not store diagnostic messages, only the last incoming diagnostic
message would be stored.
In your user program, you must query the relevant bits in device-specific diagnostic
data. Here you must take the PROFIBUS DP cycle time into account, for example,
to be able to query these bits at least once and in synchronism to bus cycle time.
With an IM 308-C operating as DP master you cannot utilize process interrupts in
device-specific diagnostics, because only incoming events are reported rather than
outgoing events.
11.6.2.1 Structure of the slave diagnostic data when the CPU
is used as an intelligent slave
Structure of the diagnostics message frame
The figure below shows the structure of the diagnostics message frame for slave
diagnostics.
S7-300 Programmable Controller Hardware and Installation
A5E00105492-02
Testing functions, Diagnostics and Fault Elimination
Order No.
6ES7313-6CE01-0AB0
6ES7314-6CF01-0AB0
6ES7315-2AG10-0AB0
From firmware version
V 2.0.0
V 2.0.0
V 2.0.0
11-23