Interrupts On The Dp Master - Siemens S7-300 Installation Manual

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If the CPU 31x-2 is used as the DP slave, you can trigger a process interrupt on
the DP master from the user program.
When you call SFC 7 "DP_PRAL", you trigger an OB40 in the user program on the
DP master. The SFC 7 allows you to forward interrupt information to the DP master
in a double word. This information can then be evaluated in the
OB40_POINT_ADDR variable in the OB 40. The interrupt information can be freely
programmed as required. The 6\VWHP VRIWZDUH IRU 6  6\VWHP DQG
6WDQGDUG )XQFWLRQV - Reference Manual contains a detailed description of SFC 7
"DP_PRAL".
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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.
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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.
S7-300 Automation System, Hardware and Installation: CPU 312IFM - 318-2 DP
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