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maersk · Member 3 Joined: 17 Aug 2014 Posts: 891

How in STEP 7 (TIA Portal) do you access the unstructured data types bit-by-bit, byte-by-byte or word-by-word and symbolically?
https://support.industry.siemens.com/cs/document/57374718/how-in-step-7- (tia-portal)-do-you-access-the-unstructured-data-types-bit-by-bit-byte-by-byte-or-word-by-word-and-symbolically

With the S7-1200/S7-1500 you can address specific areas in declared variables and access areas of the following widths: 1 bit, 8 bits, 16 bits and 32 bits.

In order to access variables of the data type Byte, Word or DWord you need
STEP 7 (TIA Portal) V11+SP1+Upd 2 (or higher) for S7-1200 (firmware V2.0 and higher).
STEP 7 (TIA Portal) V12 (or higher) for S7-1500.

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.

Access the unstructured data types bit-by-bit, byte-by-byte Access the unstructured data types bit-by-bit, byte-by-byte

Access the unstructured data types bit-by-bit, byte-by-byte Access the unstructured data types bit-by-bit, byte-by-byte

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" stands for bit-by-bit access in the Word or Byte concerned and the number that follows specifies the offset of the Bit concerned.

Access the unstructured data types bit-by-bit, byte-by-byte Access the unstructured data types bit-by-bit, byte-by-byte

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.

Access the unstructured data types bit-by-bit, byte-by-byte Access the unstructured data types bit-by-bit, byte-by-byte

A "w" stands for word-by-word slice access and the number that follows specifies the offset of the word concerned.

Access the unstructured data types bit-by-bit, byte-by-byte Access the unstructured data types bit-by-bit, byte-by-byte

In the case of some technical applications you only need the first 4 or 6 bits (Bit 0 to Bit 3 or to Bit 5 respectively) of the byte variables for converting a value of the Byte data type to a value of the Real data type. In this example a binary number (binary coded byte) is converted into a decimal number (real number). The lowest bit of the byte here has the value 2-5. This is not the places after the decimal point, but the decimal value itself that is calculated.

Access the unstructured data types bit-by-bit, byte-by-byte Access the unstructured data types bit-by-bit, byte-by-byte

In the following SCL program code the first two instructions (slice accesses) set the bits not needed to the signal "False". Then, with the data type conversion, the change is made according to the value 2-5.

Access the unstructured data types bit-by-bit, byte-by-byte Access the unstructured data types bit-by-bit, byte-by-byte

Creation Environment
The screens in this FAQ response were created with STEP 7 (TIA Portal) V13+SP1+Update 7.