Simence plc programming

PLC (Programmable Logic Controllers) Siemens
1

Hello, i want to know how interrupts work in s7 314 cpu how it divide processing time and what happen to beground process.

2

In the S7-314 CPU, interrupts are used to handle high-priority tasks that need immediate attention by temporarily suspending the main or background program. Here’s an overview of how interrupts work in this Siemens CPU, along with how it divides processing time and what happens to the background process:

1. What is an Interrupt?

An interrupt is a signal that temporarily halts the CPU’s current execution to immediately handle an urgent task (the interrupt routine). Once the interrupt routine is finished, the CPU returns to the task it was executing before the interrupt occurred.

2. Types of Interrupts in S7-314 CPU:

The S7-314 CPU can handle different types of interrupts:

  • Hardware Interrupts: Triggered by hardware events like inputs changing state or certain field devices sending signals.
  • Time Interrupts: Triggered at specific time intervals to execute a periodic task.
  • Diagnostic Interrupts: Triggered by faults or diagnostic messages from hardware.
  • Communication Interrupts: Triggered by data communications, such as messages received from a network.

3. Interrupt Handling:

  • When an interrupt occurs, the Operating System (OS) of the S7-314 CPU immediately pauses the execution of the current OB (organization block) and jumps to the interrupt OB (e.g., OB40 for hardware interrupts).
  • Once the interrupt OB is executed, the CPU resumes the interrupted task at the exact point where it was paused.

4. Processing Time Division:

  • The S7-314 CPU divides its processing time based on priority levels. Interrupt OBs have a higher priority than normal OBs, so they take precedence over background tasks.
  • Here’s the basic priority hierarchy:
    1. Interrupt OBs (e.g., OB40, OB80, etc.): Highest priority
    2. Cyclic OBs (e.g., OB1): These are executed continuously, but they can be interrupted by interrupt OBs.
    3. Background OBs (e.g., OB10): These are lower-priority tasks that run in the background when the CPU has free processing capacity.
  • During an interrupt, the CPU allocates processing power to handle the interrupt task immediately and suspends any background or cyclic tasks temporarily.

5. What Happens to the Background Process?

  • When an interrupt occurs, the CPU immediately suspends the execution of the current process (usually a cyclic OB like OB1 or a background OB).
  • The status of the background task is saved so that after the interrupt has been handled, the CPU can resume from where it left off.
  • The CPU ensures that no data or task progress is lost during this switch between processes.

6. Time Slicing and Scheduling:

  • The CPU manages time slices efficiently by using an internal scheduler. The cyclic program (usually in OB1) gets time to execute regularly but can be preempted if an interrupt OB has a higher priority.
  • Background tasks like diagnostics, communication handling, or data logging (OB10) are only processed when the CPU has completed all higher-priority tasks and there is available processing time.

7. Interrupt Priorities and Nesting:

  • If multiple interrupts occur at the same time, the CPU prioritizes them based on the predefined priority levels in the system. For instance, hardware interrupts have a higher priority than time interrupts.
  • Interrupt Nesting: The S7-314 CPU allows nested interrupts, meaning if a higher-priority interrupt occurs while a lower-priority interrupt is being processed, the CPU will temporarily suspend the lower-priority interrupt to handle the higher-priority one.

8. Configuring Interrupts:

  • In Step 7 or TIA Portal, you can configure interrupts through the PLC’s hardware configuration, setting specific OBs to handle different types of interrupts.

Interrupts in the S7-314 CPU allow the processor to immediately respond to high-priority tasks by temporarily halting normal or background processing. The CPU suspends the current task, executes the interrupt OB, and then resumes the interrupted task, ensuring efficient task handling with minimal delay. Background tasks run when no higher-priority tasks are pending.

This approach ensures that critical events are handled in real time, while regular and background processes continue in a managed, time-divided manner.

Let me know if you need more details on how to configure or troubleshoot interrupts in the S7-314!