Siemens PLC data type and address

In the following example to MD1,MD34 to MD2 MD30 (see the following figure). I entered in the simulation at MD1 30.0, press ENTER to appear 11.8953. I have no problem to do it by the book addresses. I would like to ask this MD30 into MD1,MD34 to MD2 relationship? These can literally change the address?
 
 


Here is my reply:
The address can be changed in the program, but there is one fundamental principles must be respected, that is, the same address at the same time can only be used for a single purpose, or like a person commits bigamy, big trouble!! And the problem is not easy to find out.
MD1 MB1~MB4 4bytes, MD2 MB2~MB5 4bytes, MD1 and MD2 3 bytes (MB2~MB4) overlap, use address problemstrange!


Values of MD2 and procedures relating to the implementation, MD1 MD2 MB2~MB4 depends on the value in, so after you enter a floating-point number in MD1, press the Enter key to MD1 will be changed to 11.8953.
Project does not have a few instructions for the reader to do the experiment, and less prone to address overlapping problems, there was also easy to find. In an actual project, in order to avoid using the address, you can use assignment tables in STEP 7 of the reference data to check whether a particular address is already in use, check using the cross reference table where the same address is used more than once.

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