Siemens Simatic S7-300, Hardware And Installation Manual, Page: 181 / 242

Testing functions, Diagnostics and Fault Elimination
S7-300 Programmable Controller Hardware and Installation
A5E00105492-01
10-21
10.6.3 Interrupts at the DP master
Interrupts with S7/M7 DP masters
With the CPU 31x-2 as a DP slave, you can trigger a process interrupt with the DP
master from the user program. By calling SFC7 "DP_PRIN", you will trigger an OB
40 in the user program of the DP master. You can forward interrupt information to
the DP master in a double word with the SFC7. This information can be evaluated
in OB 40 in the OB40_POINT_ADDR variable. You will find detailed information on
SFC 7 "DP_PRIN" in the reference manual System software for S7-300/400 -
System and standard functions.
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
In order to be able to evaluate diagnostic interrupts and process interrupts via
device-specific diagnostic data when operating with a different DP master, note
that:
The DP master should be able to store the diagnostic messages, that is, in its ring
buffer. 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.