Difference between V-zone and M-zone variables of Siemens S7-200PLC - Database & Sql Blog Articles

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Use a lot of bool variables, is it in V or M?

Answer: V and M basically have the same function, but the memory area of ​​V is large, so the analog value and the intermediate amount are generally stored in V, and the M area is generally used in the middle of the digital relay.
The data in the V zone has the power-off protection function. The data power-off protection range of the M zone needs to be set to be larger than the v zone, and the power-down can be saved. Other functions are similar to m.

1, V and M have no deterioration, the status is almost interchangeable;

2. V is more and M is less. Less M can make the instruction code shorter, and the storage and execution efficiency is improved.

3, M has some provisions for use, such as MB0-MB13 if set to maintain, when the power is off, it is directly written eeprom, is a permanent type of retention, except that the hold is temporarily maintained by a super capacitor or battery .

4, V capacity is large, the use of V is longer than using the M command code, of course, the time is also a bit. The same V area, I found that there are also partitions, V0-V511 is a piece, the corresponding instruction code is shorter than V512, but there is no difference in execution time, no research. Therefore, the V variable that is often used should be placed before V511 to shorten the length of the instruction code.

5, V and M due to the difference in symbols, it is customary to classify their use, such as M is mainly used as a bit variable, so the program is more readable