Siemens AG is a German multinational conglomerate company headquartered in Munich and the largest industrial manufacturing company in Europe with branch offices abroad

1. AN OVERVIEW OF SIEMENS PLC ADDRESS MAPPING
By Just Engineering

2. SIEMENS Address Mapping
We can do SIEMENS S7 mapping by two methods:
1) Direct Addressing
2) Indirect Addressing
The widely used form of addressing in SIEMENS S7 PLCs is
direct and symbolic.

3. Indirect Mapping:
Indirect address can be used to save time and money, or to automate and reduce the
source code.
If you have a PLC with 60 analog inputs, you can use an indirect address to process
information from analog inputs, such as scaling, testing alarm limit values, etc.,
meaning, for example, you don’t have to configure the alarm limit evaluation for each
signal individually.

4. The Basics of SIEMENS IO Addressing
Process Image
We can access I/O bits only through the Process image
These values are buffered in between scans
In some CPU models have limited address space

5. Peripheral Address
All address outside of the process image is referred to as peripheral address. We can’t access I/O bits
through a peripheral address
“Peripheral addressing” also means that the modules can be accessed directly. To do this, you set a “P” in
front of the address field to be addressed:
PIB --> Peripheral Input Byte
PQB --> Peripheral output Byte
PIW --> Peripheral Input Word
PQW -->Peripheral output Word
PID --> Peripheral Input Double-word
PQD --> Peripheral Output Double-word.

6. The POINTER, Data Types and Data Block Instructions
The POINTER data type is used to format a number to be recognized as an address rather than a value.
The pointer is often followed by the symbol P#. The address of the pointer can be in three different
formats.
Any data type is used to transfer a parameter of an unknown or unspecified data type. Some functions in
the library use some form of data to operate on whole portions of memory. The last pointer approach is
used to characterize the field. For eg, P#DB25.DBX address 0.0 Byte 14 points to the first byte of DB25
with a length of 14 bytes.
When operating with indirect address, it is often important to open a DB first and then start working on an
address without explicitly referring to a particular DB. This is achieved with the OPN order. The OPN
command will open either a shared data block (DB) or an instance data block (DI).

7. The Address Registers
In addition to standard accumulators, there are two 32-bit address registers (AR1, AR2) for storing pointers used in
registry indirect address methods. You may use a set of different load and switch style instructions to operate with
AR1. A similar package for AR2 is available.
Address Syntax
We need a device name and a tag address to create a tag. We need to configure the tag address. When you have
both the device name and tag address, type it in the OPC path of the Tag Editor using [device_name]:address format,
where device_name is the name of the device and address is the configured address listed there.
Tag address are the combination of three different components:
Area Syntax
Data Type Syntax
Offset Syntax

8. What is the meaning of these words?
Bits: Bits are addressed by using Bit DataType (X) and adding .bit to the end where the bit is in the range
[0-7]. When addressing a bit at a certain offset, the offset is often treated as a byte.
Timers: Timers are scaled up to the DWord and translated from the S5 time format so that they can
display the time in milliseconds without having any multipliers. When you write to a timer, it is
automatically converted from milliseconds to the S5 time format for you. A DataType is not specified
when accessing the Timer.
Strings: Strings are known to be in the S7 string format and to have a maximum length of 210.
Counters: Counters in the PLC will be processed in the BCD. The driver can automatically translate
to/from BCD for you and expose any counter tags to UInt16 values. When accessing Counters, a
DataType is not defined

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