Interrupts - Siemens SIMATIC S7-300 Series Reference Manual

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:
S
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.
S
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.
S
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.
PLC S7-300, CPU Specifications CPU 312 IFM to CPU 318-2 DP
A5E00111190-01
CPU 31x-2 as DP Master/DP Slave and Direct Communication
2-31