Symbol table of the Siemens S7-200PLC is the variable name, it is no exaggeration to say, every person using S7-200 should be familiar with it, if you laugh at it that he never used it can also do a good job, then you’re not a real programmer.
Using the symbol table, a program more readable, the allocation of resources at a glance, modify flexible input error correction and so on.
Don’t like to use the symbol table, I guess one of the reasons is probably afraid of trouble, slow. In fact, this is a misunderstanding, skilled use of symbols input table speeds are fast. Not believe it?
1. the symbol table has an AutoComplete feature, when there are several variables when used frequently, do not require memory address differences, just type the first few letters of symbol name, it will automatically prompt, so enter fast.
2. done fingering strengthening training of people should have realized, when a word or consecutive characters in the character code required even with one finger on the same hand severely affected input when the input speed, if most of the coding order of Chinese characters in an article distributed in left and right hand and typing would be much higher, and less error-prone.
Such as address variables VW3234, all left-handed enter six characters, slow and error-prone. Direct address errors is more difficult to check it out, symbol names go wrong would immediately be prompted with online, and the compiler does not pass. Symbol names to reduce the error rate is actually improving speeds.
Two symbol names using tips:
I. rapidly modify the variable address
1. the symbol name used (otherwise, the CTRL+Y switch)
2. direct modification of the symbols in the symbol table corresponding to the address of a variable
3.OK
Using the symbol table to modify access benefit data block address also changes, the find and replace works (data blocks cannot be fully replaced in the part is selected in the local area)
Second, quickly modify symbol name (such as symbol S1 is used in many places, now wants to change it to S2)
1. the symbol name is not used (if you are using before CTRL+Y switch)
2. direct modification of the symbols in the symbol table name
3.CTRL+Y, symbol name is valid
4.OK
Notice two little skill in the conditions of use of the symbol name happens to be opposite.
Because of two quick modification of the above techniques, later memory layout is very convenient. Memory location can be ignored before the programming arrangements, defines only the symbol name, memory addresses are free to enter (do not overlap, of course), which focuses on implementation and debugging features, complete memory requirements, to cut and paste the symbol name to adjust the sort, and finally fill with Excel features a continuous address, to which a program uses memory, see symbol table at a glance.
Add an alternative “technique“, sometimes using this method than a search for accurate and efficient
Sometimes need to quickly determine whether a variable or timer repeat use, such as the VW100
1. assuming that the VW100 symbol name is S1 (without defined one), the symbol names in use
2. direct modification of the symbol name is an undefined symbol (for example, just add a suffix after) S1_ttttt
3. coding code (not all compiled), the following error number in the output window (if 1 there is only 1 Reference)
4. scroll the output window, double-click the error prompt, you can quickly navigate to the reference
5. switch to the symbol table to withdraw to modify
This method checks a convenience when viewing multiple variables in a row reference number, the interface does not need to switch (using the Find method will change the current cursor).
PLC ONE 