CPU 31x-2 as DP Master/DP Slave and Direct Communication
2-31
PLC S7-300, CPU Specifications CPU 312 IFM to CPU 318-2 DP
A5E00111190-01
2.6.10 Interrupts
Interrupts with S7/M7 DP Master
You can trigger a process interrupt at the DP Master in the user program of a CPU
31x-2 operating as DP Slave. A call of SFC 7 “DP_PRAL” triggers an OB40 in the
user program of the DP Master. SFC 7 allows you to forward interrupt information
in a DWORD to the DP master; this information can then be evaluated in OB 40 in
variable OB40_POINT_ADDR. You can program the interrupt information as
desired. A detailed description of SFC 7 “DP_PRAL” can be found in the reference
manual entitled System Software S7-300/400 - System and Standard Functions.
Interrupts with Another DP Master
If you are running the CPU 31x-2 with another DP master, these interrupts are
reflected in the station diagnosis of the CPU 31x-2. You must post-process the
relevant diagnostic events in the DP master’s user program.
Note
When evaluating diagnostic/process interrupts with another DP Master via
device-specific diagnostics, take into consideration:
The DP master should be able to store the diagnostic messages, that is, the
DP master should have a ring buffer in which to place these messages. If the
DP master can not store diagnostic messages, only the last diagnostic
message would be available for evaluation.
You must scan the relevant bits in the device-related diagnostic data in your
user program at regular intervals. You must also take the PROFIBUS-DP’s bus
cycle time into consideration so that you can scan the bits at least once in sync
with the bus cycle time, for example.
With an IM 308-C operating as DP Master, you cannot use process interrupts
in a device-specific diagnosis because only incoming interrupts are reported,
rather than outgoing interrupts.
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