In the case of S7-1200 modules (as from firmware V2.0) you have the option of accessing bit-by-bit the tags of the Byte, Word and DWord data types. For this you need STEP 7 V11+SP1+Update 2 (or higher). The partitioning of a memory area (Byte or Word, for example) into a smaller memory area (Bool, for example) is also called memory slicing. Fig. 01 shows the symbolic bit, byte and word access to operands.
Using slice access provides you with greater programming efficiency and there is no need for additional definition in the variable declaration.
The example below shows bit-by-bit symbolic slice access. The "x" stand for bit-by-bit access in the word or byte concerned and the number that follows specifies the offset of the bit concerned.
Fig. 03 shows a sample byte-by-byte slice access. Here, the "b" stands for byte-by-byte access and the number that follows specifies the offset of the byte concerned.
A "w" stands for word-by-word slice access and the number that follows specifies the offset of the word concerned.