For example, let the value 68 be assigned to doublewords, words and bytes, and the storage results of doublewords, words and bytes are all 68.

1, you assign 68=VB 120. The result byte VB 120=68.

2. You assign 68=VB 120. If VB 1 19 is not used, the word VW 1 19=68 (high byte 0=VB 1 19, low byte 68 = VB 65438). The result word VW 1 19=68.

3. You assign 68=VB 120, but you don't use VB 1 19, VB 1 18, VB 1 17, so the double word VD/kloc. The second high byte VB 1 18=0, the second high byte VB 1 19=0, and the lowest byte VB 120=68). Results The double word VD 1 17=68.

Extension:

This example shows that the low-order data of Siemens PLC words and double-word bytes are placed in the high-order byte unit; The high-order data is placed in the low-order byte unit.

Conclusion:

Therefore, Siemens PLC does not need byte-to-byte, word-to-word, and double-word module functions (neither), that is, how to store and read. Note that once the read mode conversion is used, the memory interval unit used in the read mode conversion cannot be written into data by other program segments before its use function is realized, otherwise the converted data will be confused. Therefore, Siemens PLC has given thousands to tens of thousands of bytes of storage units, which are generally enough for you to convert and use at will. The same is true of other models of PLC from different manufacturers, with several different high and low positions and the same principle.