Accessing A "Slice" Of A Tagged Data Type - Siemens SIMATIC S7-1200 Manual

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4.4 Memory areas, addressing and data types
Configuring the I/O in the CPU and I/O modules
The figure shows an example of a CPU 1214C with two SMs and one SB. In this example,
you could change the address of the DI8 module to 2 instead of 8. The tool assists you by
changing address ranges that are the wrong size or conflict with other addresses.
4.4.3

Accessing a "slice" of a tagged data type

PLC tags and data block tags can be accessed at the bit, byte, or word level depending on
their size. The syntax for accessing such a data slice is as follows:
● "<PLC tag name>".xn (bit access)
● "<PLC tag name>".bn (byte access)
● "<PLC tag name>".wn (word access)
● "<Data block name>".<tag name>.xn (bit access)
● "<Data block name>".<tag name>.bn (byte access)
● "<Data block name>".<tag name>.wn (word access)
A double word-sized tag can be accessed by bits 0 - 31, bytes 0 - 3, or word 0 - 1. A word-
sized tag can be accessed by bits 0 - 15, bytes 0 - 1, or word 0. A byte-sized tag can be
accessed by bits 0 - 7, or byte 0. Bit, byte, and word slices can be used anywhere that bits,
bytes, or words are expected operands.
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When you add a CPU and I/O modules to your
configuration screen, I and Q addresses are
automatically assigned. You can change the
default addressing by selecting the address field in
the device configuration and typing new numbers.
• Digital inputs and outputs are assigned in
groups of 8 points (1 byte), whether the module
uses all the points or not.
• Analog inputs and outputs are assigned in
groups of 2 points (4 bytes).
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Manual, 03/2014, A5E02486774-AF