Time Error Interrupt Ob - Siemens S7-1200 System Manual

PLC concepts
4.1 Execution of the user program
Hardware interrupt events
Changes in the hardware, such as a rising or falling edge on an input point, or an HSC (High
Speed Counter) event trigger hardware interrupt events. The S7-1200 supports one interrupt
OB for each hardware interrupt event. You enable the hardware events in the device
configuration, and assign an OB for an event in the device configuration or with an ATTACH
instruction in the user program. The CPU supports several hardware interrupt events. The
CPU model and the number of input points determine the exact events that are available.
Limits on hardware interrupt events are as follows:
Edges:
● Rising edge events: maximum of 16
● Falling edge events: maximum of 16
HSC events:
● CV=PV: maximum of 6
● Direction changed: maximum of 6
● External reset: maximum of 6
4.1.3.6

Time error interrupt OB

If configured, the time error interrupt OB (OB 80) executes when either the scan cycle
exceeds the maximum cycle time or a time error event occurs. If triggered, it executes,
interrupting normal cyclic program execution or any other event OB.
The occurrence of either of these events generates a diagnostic buffer entry describing the
event. The diagnostic buffer entry is generated regardless of the existence of the time error
interrupt OB.
Time error interrupt events
The occurrence of any of several different time error conditions results in a time error event:
● Scan cycle exceeds maximum cycle time
The "maximum cycle time exceeded" condition results if the program cycle does not
complete within the specified maximum scan cycle time. See the section on "Monitoring
the cycle time in the S7-1200 System Manual" (Page 97) for more information regarding
the maximum cycle time condition, how to configure the maximum scan cycle time in the
properties of the CPU, and how to reset the cycle timer.
● CPU cannot start requested OB because a second time interrupt (cyclic or time-delay)
starts before the CPU finishes execution of the first interrupt OB
● Queue overflow occurred
The "queue overflow occurred" condition results if the interrupts are occurring faster than
the CPU can process them. The CPU limits the number of pending (queued) events by
using a different queue for each event type. If an event occurs when the corresponding
queue is full, the CPU generates a time error event.
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S7-1200 Programmable controller
System Manual, 03/2014, A5E02486680-AG