Siemens SIMATIC S7-1200 - Page 108

PLC concepts
5.1 Execution of the user program
S7-1200 Programmable controller
108 System Manual, V4.2, 09/2016, A5E02486680-AK
Event
Quantity allowed
Default OB priority
MC-Servo
1 event
25
MC-Interpolator 1 event 24
1
The startup event and the program cycle event never occur at the same time because the startup
event runs to completion before the program cycle event starts.
2
You can have more than 50 hardware interrupt event OBs if you use the DETACH and ATTACH
instructions.
3
You can configure the CPU to stay in RUN if the scan cycle exceeds the maximum scan cycle time
or you can use the RE_TRIGR instruction to reset the cycle time. However, the CPU goes to
STOP mode the second time that one scan cycle exceeds the maximum scan cycle time.
4
The priority for a new V4.0 or V4.1 CPU is 22. If you exchange a V3.0 CPU for a V4.0 or V4.1
CPU, the priority is 26: the priority that was in effect for V3.0. In either case, the priority field is ed-
itable and you can set the priority to any value in the range 22 to 26.
Refer to the topic "Exchanging a V3.0 CPU for a V4.1 CPU (Page 1571)" for more details.
In addition, the CPU recognizes other events that do not have associated OBs. The following
table describes these events and the corresponding CPU actions:
Table 5- 17 Additional events
Event
Description
CPU action
I/O access error Direct I/O read/write error The CPU logs the first occurrence in the
diagnostic buffer and stays in RUN mode.
You can access the error cause using the
GET_ERROR_ID (Page 311) instruction.
Max cycle time error CPU exceeds the configured
cycle time twice
The CPU logs the error in the diagnostic
buffer and transitions to STOP mode.
Peripheral access error I/O error during process im-
age update
The CPU logs the first occurrence in the
diagnostic buffer and stays in RUN mode.
Programming error program execution error
• If block-local error handling is enabled,
the system enters an error cause in the
error structure. You can access the er-
ror cause using the GET_ERROR_ID
(Page 311) instruction.
• If global error handling is enabled, the
system enters an access error start
event into the diagnostic buffer and
stays in RUN mode.
Interrupt latency
The interrupt event latency (the time from notification of the CPU that an event has occurred
until the CPU begins execution of the first instruction in the OB that services the event) is
approximately 175 µsec, provided that a program cycle OB is the only event service routine
active at the time of the interrupt event.