How to use the symbol table in Siemens PLC programming - Database & Sql Blog Articles

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In the plc programming software specification, variable naming itself is a matter of learning.
The symbol table of Siemens S7-200PLC is to do variable naming work. It is no exaggeration to say that everyone who uses S7-200 should be proficient in it. If you dismiss it, you can use it without you. Well done, then you can't be a real programmer.
Using the symbol table, there are programs that are more readable, resource allocation at a glance, flexible modification, and input error correction.
I don't like to use the symbol table. One of the reasons I guess may be that I am afraid of trouble and slow. In fact, this is a misunderstanding of understanding. After using the symbol table skillfully, the input speed is faster. Don't believe it?
1. The symbol table has an auto-complete function. When several variables are frequently used alternately, there is no need to memorize the address difference. Only the first few letters of the symbol name need to be typed, and the prompt will be automatically prompted, so the input is faster.
2. People who have done fingering intensive training should have the experience that when a word or Chinese character code has continuous characters that need to be input with the same hand or even the same finger, the input speed is seriously affected, if the Chinese characters in an article are mostly encoded. They are all distributed in the left and right hands, the input speed will be much higher, and it is not easy to make mistakes.
For example, the address variable VW3234, all six characters use left-hand input, the speed is slow, and error-prone. It is more difficult to check out the direct address error. If the symbol name is wrong, there will be an online prompt, and the compilation will not pass. The symbol name reduces the error rate and actually increases the speed.
Tips for using two symbolic names:
1. Quickly modify the variable address (posted in another post)
1. The symbol name is in use (otherwise, CTRL+Y switch first)
2. Modify the variable address corresponding to the symbol directly in the symbol table. 3.OK
There is an advantage in using the symbol table to modify the address. The address in the data block will also be modified at the same time. This is better than the search replacement. (The data block cannot be selected and replaced in the local scope.)
Second, quickly modify the symbol name (for example, the symbol name S1 has been used in multiple places, now I want to change it to S2)
1. The symbol name is not used (if it is in use, first CTRL+Y switch)
2. Modify the symbol name directly in the symbol table 3.CTRL+Y, the symbol name is valid 4.OK
Note that in the above two tips, the condition in which the symbol name is used is exactly the opposite.
Because of the two quick-modification techniques above, post-memory planning is very convenient. Before programming, you can not consider the memory location arrangement, only define the symbol name, the memory address can be input casually (of course, do not overlap), so focus on the function implementation and debugging, after the completion of the memory planning requirements, the symbol name cut and paste to adjust the sort, Finally, use the Excel fill function to continuously generate addresses. Which memory is used by a program, look at the symbol table at a glance.
Add a different kind of "skills", sometimes using this method is more efficient than searching. Sometimes you need to quickly determine whether a variable or timer is reused, such as VW100.
1. Assume that the symbol name of VW100 is S1 (if no one is defined), make the symbol name in use 2. Directly modify the symbol name to an unused symbol (such as adding a suffix later) to S1_ttttt
3. Encoding code (not all compiled), the following output window prompts the number of errors (if there is 1 there is only one reference)
4. Scroll the output window, double-click the error prompt line, you can quickly locate the reference point. 5. Switch to the symbol table and undo the modification. This method is convenient when you need to check the number of multiple variable references continuously. The interface does not need to be switched. Will constantly change the current cursor).