Hello everyone, I am Dog Brother! Today, let's talk about a super useful feature in Siemens PLC—interrupt programming. Interrupts allow our PLC programs to be more flexible, respond faster to unexpected events, and increase efficiency. Whether you are a beginner or have been in the field for a while, mastering interrupt programming will definitely elevate your skills! So, fasten your seatbelts, and let's start today's learning journey!
## 1. What is an Interrupt?
An interrupt, as the name suggests, is a mechanism that "interrupts" the currently executing program to prioritize certain specific events. Imagine you're watching TV, and suddenly the doorbell rings. You would pause the TV, go open the door, and then come back to continue watching. This is a "interrupt" in real life!
In PLCs, interrupts allow us to define special program blocks that, under specific conditions (like a signal change, timer expiration, etc.), the PLC will immediately stop its current work, execute this special program block, and then return to continue its previous work.
<strong>Tip</strong>: The execution speed of interrupt programs is very fast, usually completed within a few milliseconds, so it has minimal impact on the main program.
## 2. Why Use Interrupts?
1. <strong>Fast Response</strong>: For events that need immediate handling, interrupts ensure the fastest response speed.
2. <strong>Increased Efficiency</strong>: No need to constantly check certain conditions in the main program, saving CPU resources.
3. <strong>Simplified Programs</strong>: Separating special handling from the main program makes the program structure clearer.
Imagine you are responsible for a production line in a factory. Normally, you complete your daily tasks step by step. But if there is an emergency (like equipment failure), you will immediately put down your work to address it. This is the role of interrupts!
## 3. Types of Interrupts in Siemens PLC
Siemens PLC provides various types of interrupts; let's get to know a few common ones:
1. <strong>Hardware Interrupts</strong>: Triggered by external signals, such as button presses, sensor signals, etc.
2. <strong>Timer Interrupts</strong>: Triggered periodically at set time intervals.
3. <strong>Diagnostic Interrupts</strong>: Triggered when the PLC detects a fault.
4. <strong>Clock Interrupts</strong>: Triggered at specific clock times, such as every hour.
<strong>Note</strong>: The types of interrupts supported may vary by model of Siemens PLC, so be sure to consult the relevant manual before use!
## 4. How to Use Interrupts?
Now that we understand the theoretical knowledge, let’s see how to implement it in practice! We will take hardware interrupts as an example and write a simple interrupt program together.
Assuming we want to detect whether products on the production line are qualified. When an unqualified product is detected, we immediately stop the conveyor belt and sound an alarm.
1. We need to configure the hardware interrupt. In the hardware configuration, assign an interrupt to a channel of the digital input module.
2. Create an interrupt organization block (OB). For hardware interrupts, we use OB40.
3. Write the interrupt handling program in OB40:
// Hardware Interrupt Handling Program OB40ORGANIZATION_BLOCK OB40VAR_TEMPOB40_EV_CLASS ： BYTE; // Interrupt CategoryOB40_STRT_INF ： BYTE; // Interrupt InformationOB40_IO_FLAG ： BYTE; // Input Module/Output ModuleOB40_MDL_ADDR ： WORD; // Module Starting AddressOB40_INP_ADDR ： WORD; // Interrupt Input AddressOB40_RESERVED_1 ： BYTE; // ReservedEND_VAR
BEGIN// Stop the Conveyor BeltQ0.0 := FALSE;
// Activate Alarm LightQ0.1 := TRUE;
// Record Number of Unqualified ProductsCOUNT_BAD_PRODUCTS(); // Assume this is a custom counter functionEND_ORGANIZATION_BLOCK
In this example, when an unqualified product is detected (triggering the hardware interrupt), the program will immediately stop the conveyor belt, turn on the alarm light, and record the number of unqualified products.
<strong>Tip</strong>: Interrupt programs should be kept as short as possible, only handling the most critical tasks. Complex processing logic is best placed in the main program.
## 5. Interrupt Priority
In Siemens PLC, different types of interrupts have different priorities. When multiple interrupts occur simultaneously, the PLC will first execute the one with the higher priority.
Generally, the priority from high to low is:
1. Hardware Interrupts
2. Diagnostic Interrupts
3. Timer Interrupts
4. Cyclic Programs (Main Program)
<strong>Note</strong>: While interrupts can improve the program's response speed, excessive use of interrupts may affect the execution of the main program. Use them wisely based on actual needs!
## 6. Enabling and Disabling Interrupts
Sometimes, we may need to temporarily disable certain interrupts. Siemens PLC provides corresponding instructions:
// Disable All InterruptsDINT;
// Enable All InterruptsENIT;
// Disable Specific InterruptDISABLE_INTERRUPTS(OB_NR := 40);
// Enable Specific InterruptENABLE_INTERRUPTS(OB_NR := 40);
These instructions allow us to flexibly control the triggering of interrupts, dynamically adjusting the program's behavior when needed.
## Practice Time!
Let’s do a little practice to reinforce our understanding:
1. Design a program using timer interrupts to check the temperature sensor’s value every 5 seconds. If the temperature exceeds 80 degrees, trigger an alarm.
2. Think about in what industrial scenarios interrupt programming is particularly useful? Feel free to share your thoughts in the comments!
## Summary
Today we learned the basics of Siemens PLC interrupt programming. We understood what interrupts are, why to use them, the types of interrupts in Siemens PLC, and how to write and use interrupt programs. Interrupt programming is a powerful tool that can make our PLC programs more flexible and efficient, allowing for timely handling of unexpected events.
Remember, practice makes perfect! Try different types of interrupts, apply them flexibly in actual projects, and you will become a master of interrupt programming!
Friends, our learning journey on Siemens PLC ends here today! Remember to get hands-on with coding, and feel free to ask Dog Brother any questions in the comments. I wish everyone happy learning and continuous improvement in Siemens PLC!