When working with PLC programming software, variable naming is an essential skill that often gets overlooked. In the case of Siemens S7-200 PLCs, the symbol table plays a crucial role in managing variable names. It's safe to say that anyone using this system should become proficient in it. Dismissing the symbol table might seem harmless at first, but if you don’t use it effectively, you’ll find it difficult to be a real programmer.
Using the symbol table offers several advantages. It makes your code more readable, allows for quick resource allocation, simplifies modifications, and helps catch input errors early. Some people avoid it because they think it’s time-consuming or complicated, but this is a common misconception. Once you get used to it, you'll find that the auto-complete feature can actually speed up your work significantly.
For example, when dealing with frequently used variables, you don’t need to remember their exact addresses. Just type the first few letters of the symbol name, and the system will suggest possible matches. This not only saves time but also reduces errors.
Another benefit is that using symbols instead of direct addresses improves readability and reduces the chance of mistakes. Imagine typing "VW3234" repeatedly—this can be slow and error-prone. If the symbol name is incorrect, the system will flag it during compilation, making debugging easier.
Here are some tips for efficiently using the symbol table:
- Quickly Modify Variable Addresses: If a symbol is in use, switch it off using CTRL+Y. Then, directly edit the address in the symbol table and save the changes. This updates all references in the data block automatically, which is much better than manual search-and-replace.
- Modify Symbol Names Efficiently: If a symbol like "S1" is used in multiple places and needs to be changed to "S2," make sure it's not in use. Edit the symbol name directly, then press CTRL+Y to apply the change. This method avoids confusion and keeps your code consistent.
These techniques make memory planning much easier. You can define symbol names first and assign addresses later, without worrying about overlaps. After finishing the logic, you can rearrange the symbols and even use Excel to generate sequential addresses quickly.
Additionally, there's a useful trick for checking how many times a variable is used. For instance, if you want to see if "VW100" is reused, you can temporarily rename it (like "S1_ttttt") and compile the program. The error window will show how many times it was referenced, allowing you to locate each instance quickly without switching between windows.
Overall, the symbol table isn't just a convenience—it's a powerful tool that enhances productivity, accuracy, and maintainability in PLC programming. Embracing it can transform the way you approach your projects, making your coding process smoother and more efficient.
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