Siemens Memory Specifications

Background and system description 03/2014
Programming Guideline for
S7-1200/1500
STEP 7 (TIA Portal)
http://support.automation.siemens.com/WW/view/en/81318674
Warranty and liability
Warranty and liability
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Programming Guideline for S7-1200/1500
Entry-ID: 81318674, V1.2, 03/2014
2
Table of contents
Table of contents
Siemens AG 2014 All rights reserved
Warranty and liability................................................................................................... 2
1
Preface ................................................................................................................ 5
2
S7-1200/1500 Innovations ................................................................................. 6
2.1
2.2
2.3
2.4
2.5
2.6
2.6.1
2.6.2
2.6.3
2.6.4
2.6.5
2.7
2.8
2.8.1
2.8.2
2.8.3
2.9
2.9.1
2.9.2
2.9.3
2.10
2.11
2.12
2.13
3
Introduction ........................................................................................... 6
Terms ................................................................................................... 6
Programming languages ...................................................................... 8
Optimized machine code ...................................................................... 8
Block creation ....................................................................................... 9
Optimized blocks ................................................................................ 10
S7-1200: Setup of optimized blocks................................................... 10
S7-1500: Setup of optimized blocks................................................... 11
Best possible data storage in the processor on S7-1500 .................. 12
Conversion between optimized and non-optimized tags ................... 15
Communication with optimized data .................................................. 16
Block sizes ......................................................................................... 17
New data types for S7-1200/1500 ...................................................... 17
Elementary data types........................................................................ 17
Date_Time_Long data type ................................................................ 18
VARIANT data type ............................................................................ 18
Instructions ......................................................................................... 20
CALCULATE ...................................................................................... 20
MOVE instructions .............................................................................. 20
RUNTIME ........................................................................................... 21
Symbolic and comments .................................................................... 22
System constants ............................................................................... 23
Internal reference ID for controller and HMI tags ............................... 24
STOP mode in the event of errors ..................................................... 25
General Programming ..................................................................................... 27
3.1
3.2
3.2.1
3.2.2
3.2.3
3.2.4
3.2.5
3.2.6
3.2.7
3.2.8
3.3
3.3.1
3.3.2
3.4
3.4.1
3.4.2
3.4.3
3.4.4
3.5
3.6
3.6.1
3.6.2
3.6.3
3.6.4
3.6.5
Operating system and user program .................................................. 27
Program blocks .................................................................................. 27
Organization blocks (OB) ................................................................... 28
Functions (FC) .................................................................................... 30
Function blocks (FB) .......................................................................... 32
Instances ............................................................................................ 33
Multi-instances ................................................................................... 33
Global data blocks (DB) ..................................................................... 35
Downloading without reinitialization ................................................... 36
Reusability of blocks........................................................................... 39
Block interface types .......................................................................... 40
Call-by-value with In interface type .................................................... 40
Call-by-reference with InOut interface type ........................................ 41
Storage concept ................................................................................. 41
Block interfaces as data exchange .................................................... 41
Global memory ................................................................................... 42
Local memory ..................................................................................... 43
Access speed of memory areas ......................................................... 44
Retentivity ........................................................................................... 45
Symbolic addressing .......................................................................... 47
Symbolic instead of absolute addressing ........................................... 47
ARRAY data type and indirect field accesses .................................... 49
STRUCT data type and PLC data types ............................................ 51
Access to I/O areas with PLC data types ........................................... 52
Slice access ....................................................................................... 53
Programming Guideline for S7-1200/1500
Entry-ID: 81318674, V1.2, 03/2014
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Table of contents
3.7
3.7.1
3.7.2
3.7.3
3.7.4
3.8
3.9
3.10
3.10.1
3.10.2
3.10.3
3.10.4
3.10.5
3.10.6
3.10.7
3.10.8
4
Hardware-Independent Programming ........................................................... 69
4.1
4.2
4.3
Siemens AG 2014 All rights reserved
Libraries .............................................................................................. 54
Types of libraries and library elements .............................................. 54
Type concept ...................................................................................... 56
Differences for typifiable objects for controller and HMI .................... 56
Versioning of a block .......................................................................... 57
Process interrupts .............................................................................. 61
Other performance recommendations ............................................... 63
SCL programming language: Tips and tricks ..................................... 64
Using call templates ........................................................................... 64
What instruction parameters are mandatory? .................................... 65
Drag & drop with entire tag names..................................................... 65
Efficiently inserting CASE instruction ................................................. 66
No manipulation of loop counters for FOR loop ................................. 66
FOR loop backwards .......................................................................... 67
Simple creating of instances for calls ................................................. 67
Handling of time tags.......................................................................... 67
Data types of S7-300/400 and S7-1200/1500 .................................... 69
No bit memory but global data blocks ................................................ 70
Programming of "clock bits" ............................................................... 71
5
The Most Important Recommendations ........................................................ 72
6
Related Literature ............................................................................................ 73
7
History............................................................................................................... 74
Programming Guideline for S7-1200/1500
Entry-ID: 81318674, V1.2, 03/2014
4
1 Preface
1
Preface
Aims for the development of the new SIMATIC control generation
An engineering framework for all automation components (controller, HMI,
drives, etc.)
Uniform programming
Increased performance
Full set of commands for every language
Fully symbolic program generation
Data handling even without pointer
Reusability of created blocks
Aim of the guideline
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The new control generation SIMATIC S7-1200 and S7-1500 has an up-to-date
system architecture, and together with the TIA Portal offers new and efficient
options of programming and configuration. It is no longer the resources of the
controller (e.g. data storage in the memory) that are paramount but the actual
automation solution.
This document gives you many recommendations and tips on the optimal
programming of S7-1200/1500 controllers. Some differences in the system
architecture of the S7-300/400, as well as the thus connected new programming
options are explained in an easy to understand way. This helps you to create a
standardized and optimal programming of your automation solutions.
The examples described can be universally used for the controllers S7-1200 and
S7-1500.
Core content of this programming guideline
The following key issues on the TIA Portal are dealt with in this document:
S7-1200/1500 innovations
–
Programming languages
–
Optimized blocks
Recommendation on general programming
–
Operating system and user program
–
Storage concept
–
Symbolic addressing
–
Libraries
Recommendations on hardware-independent programming
Advantages and benefits
Numerous advantages arise by applying these recommendations and tips:
Powerful user program
Clear program structures
Intuitive and effective programming solutions
Programming Guideline for S7-1200/1500
V1.2, Entry ID: 81318674
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2 S7-1200/1500 Innovations
2.1 Introduction
2
S7-1200/1500 Innovations
2.1
Introduction
In general, the programming of SIMATIC controllers has stayed the same from S7300/400 to S7-1500. There are the familiar programming languages such as LAD,
FBD, STL, SCL or graph and blocks such as organization blocks (OBs), function
blocks (FBs), functions (FCs) or data blocks (DBs). I.e. already created S7-300/400
programs can be implemented on S7-1500 and already created LAD, FBD and
SCL programs on S7-1200 controller without any problems.
Additionally, there are many innovations that make programming easier for you and
which allow a powerful and storage-saving code.
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We not only recommend implementing programs that are implemented for S71200/1500 controllers 1:1 but also to check them for the new options and where
applicable, to use them. The additional effort is often limited and you get a program
code that is, for example,
2.2
•
optimal in terms of memory and runtime for the newer CPUs
•
easier to understand,
•
and easier to maintain.
Terms
General terms using TIA Portal
Some terms have changed in order to make better handling with the TIA Portal
possible.
Figure 2-1: New terms in the TIA Portal
STEP 7 V5.x
STEP 7 (TIA Portal)
Symbol table
PLC tags
UDT
PLC data types
VAT table
Watch table
Terms for tags and parameters
When it is about tags, functions, and function blocks, many terms are repeatedly
used differently or even incorrectly. The following figure is to clarify these terms.
Programming Guideline for S7-1200/1500
V1.2, Entry ID: 81318674
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2 S7-1200/1500 Innovations
2.2 Terms
Figure 2-2: Terms associated with tags and parameters
Global DB
2
FC / FB
1
3
4
Table 2-1: Terms associated with tags and parameters
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Term
Note
Description
1.
Tag
Tags are reserved memory areas for values in the
controller. Tags are always defined with a certain data
type (Bool, Integer, etc.):
PLC tags
Single tags in data blocks
Complete data blocks
2.
Tag value
Tag values are values stored in a tag (e.g., 15 as value
of an Integer tag).
3.
Actual parameter
Actual parameters are tags interconnected at the
interfaces of instructions, functions, and function blocks.
4.
Formal parameter
(transfer parameter,
block parameter)
Formal parameters are the interface parameters of
instructions, functions, and function blocks (Input,
Output, InOut, Temp, Static, and Return).
You will find further information in the following entries:
What entries are available on the internet for the migration to STEP 7 (TIA
Portal) and WinCC (TIA Portal)?
http://support.automation.siemens.com/WW/view/en/58879602
What prerequisites have to be fulfilled in order to migrate a STEP 7 V5.x project
into STEP 7 Professional (TIA Portal)?
http://support.automation.siemens.com/WW/view/en/62101406
PLC migration for S7-1500 with STEP 7 (TIA Portal) V12
http://support.automation.siemens.com/WW/view/en/67858106
Programming recommendations for S7-1200 and S7-1500 with STEP 7 (TIA
Portal) V12
http://support.automation.siemens.com/WW/view/en/67582299
Why is it not possible to mix register passing and explicit parameter transfer with
the S7-1500 in STEP 7 (TIA Portal) V12?
Among others, the migration of STL programs to S7-1500 is described in this
entry.
http://support.automation.siemens.com/WW/view/en/67655405
Programming Guideline for S7-1200/1500
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2.3 Programming languages
2.3
Programming languages
For the programming of a user program, various different programming languages
are available. Each language has its own advantages, which can be variably used,
depending on the application. Every block in the user program can therefore be
created in any programming language.
Table 2-2: Programming languages
Programming language
S7-1200
S7-1500
Ladder (LAD)
Function block diagram (FBD)
Structured control language (SCL)
Graph
planned
Statement list (STL)
Note
You will find further information in the following entries:
Siemens AG 2014 All rights reserved
SIMATIC S7-1200 / S7-1500 Comparison list for programming languages
http://support.automation.siemens.com/WW/view/en/86630375
What has to be observed when migrating a S7-SCL program in STEP 7
(TIA Portal)?
http://support.automation.siemens.com/WW/view/en/59784006
What instructions cannot be used in STEP 7 V11 in an SCL program?
http://support.automation.siemens.com/WW/view/en/58002710
Copyright
How can the constants be defined under STEP 7 V11 in a S7-SCL program?
http://support.automation.siemens.com/WW/view/en/58065411
2.4
Optimized machine code
TIA Portal and S7-1200/1500 allow an optimized runtime performance in any
programming language. All languages are compiled the same, directly into the
machine code.
Advantages
All programming languages have the same high performance (with the same
access types)
No reduced performance through additional compiling with an intermediate
step via STL
Properties
The following figure displays the difference of the compilation of S7 programs into
machine code.
Programming Guideline for S7-1200/1500
V1.2, Entry ID: 81318674
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2.5 Block creation
Figure 2-3: Machine code generation with S7-300/400/WinAC and S7-1200/1500
S7-1200/1500
S7-300/400/WinAC
SCL
LAD
FBD
SCL
LAD
FBD
STL
(only S7-1500)
STL
Machine code
S7-300/400/WinAC
Machine code
S7-1200/1500
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For S7-300/400/WinAC controllers LAD and FBD programs are first of all
compiled in STL before the machine code is created.
For S7-1200/1500 controllers all programming languages are directly compiled
into machine code.
2.5
Block creation
All blocks such as OBs, FBs and FCs can be programmed directly in the desired
programming language. Thus no source has to be created for SCL programming.
You only select the block, and SCL as programming language. The block can then
be directly programmed.
Figure 2-4: “Add new block” dialog
Programming Guideline for S7-1200/1500
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2.6 Optimized blocks
2.6
Optimized blocks
S7-1200/1500 controllers have optimized data storage. In optimized blocks, all tags
are automatically sorted by their data type. The sorting ensures that data gaps
between the tags are minimized and that the tags are stored access-optimized for
the processor.
Non-optimized blocks only exist for reasons of compatibility in S7-1200/1500.
Advantages
The access is always as fast as possible, since the file storage is optimized by
the system and is independent of the declaration.
No danger of inconsistencies due to faulty, absolute accesses since the access
is generally symbolic.
Declaration changes do not lead to access errors since, for example, HMI
accesses are performed symbolically.
Individual tags can be specifically defined as “retain”.
Memory reserves in the data block make it possible to change the actual
values without any loss (see chapter 3.2.7 Downloading without reinitialization)
2.6.1
S7-1200: Setup of optimized blocks
Figure 2-5: Optimized block of S7-1200
Standard block
Bits
Standard
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No settings in the instance data block are necessary. Everything is set in the
assigned FB (e.g. retentivity).
0
0
1
2
2
4
B1
X2
X3
3
4
6
0
7
1
2
3
4
5
6
7
W1
B
y
t
e
s
W2
B1
W1
5
6
Optimized
5
X1
1
B
y
t
e
s
3
Optimized block
Bits
X1
X2
X3
X4
X3
7
8
9
W2
Properties
No data gaps are formed since larger tags are located at the beginning of the
block and smaller ones at the end.
Only the symbolic access exists for optimized blocks.
Programming Guideline for S7-1200/1500
V1.2, Entry ID: 81318674
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2.6 Optimized blocks
2.6.2
S7-1500: Setup of optimized blocks
Figure 2-6: Optimized block of S7-1500
Standard
Standard block
Bits
0
0
1
2
3
2
Optimized
4
5
6
0
7
2
3
4
5
6
7
W1
B1
X2
B
y
t
e
s
X3
3
4
W1
5
6
1
X1
1
B
y
t
e
s
Optimized block
Bits
W2
B1
X1
X2
X4
X3
7
X4
8
W2
9
Reserve
Siemens AG 2014 All rights reserved
Figure 2-7: Memory space assignment in optimized blocks
Optimized
4 Byte are always read at once
DW
0
16
Copyright
B
y
t
e
s
W
W
DW
W
W
B
1
W
W
B B B B X X X
Reserve
32
48
64
80
96
DW
102
128
W
B X X
DW
DW
W
W
2
Reserve
144
1. Structures are stored separately and can thus be copied as one block.
2. Retentive data are stored in a separate area and can be copied as one block.
In the event of a power failure, these data are stored CPU-internally. "MRES"
resets these data to the start values stored in the load memory.
Properties
No data gaps are formed since larger tags are located at the beginning of the
block and smaller ones at the end.
Fast access due the best possible storage in the processor (All tags are stored
in a way so that the processor of the S7-1500 can directly read or write all tags
with just one machine command).
Boolean tags are stored as byte for faster access. The controller therefore
does not have to mask the access.
Programming Guideline for S7-1200/1500
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2 S7-1200/1500 Innovations
2.6 Optimized blocks
Optimized blocks have a memory reserves for reloading in running operation
(see chapter 3.2.7 Downloading without reinitialization).
Only the symbolic access exists for optimized blocks.
2.6.3
Best possible data storage in the processor on S7-1500
For reasons of compatibility to the first SIMATIC controllers the “Big-Endian”
principle of data storage was adopted in the S7-300/400 controllers.
The new S7-1500 controller generation always accesses 4 byte (32 bit) in “LittleEndian” sequence due to the changed processor architecture. This results in the
following system-specific properties.
Figure 2-8: Data access of a S7-1500 controller
Bits
Standard
0
1
2
Siemens AG 2014 All rights reserved
4
5
6
7
Conversion for
processor access:
Big Little Endian
1
2
0
3
1
4
2
5
3
6
X
7
Copyright
3
BYTE
0
B
y
t
e
s
Optimized block
max. 16MB
8
0
9
1
REAL
Big-Endian
X
1
2
Copying requires time due to resorting!
Standard block
max. 64kB
WORD
Big-Endian
Bits
Optimized
0
1
2
3
3
2
B
y
t
e
s
REAL
1
4
5
6
7
Best possible processor
data storage:
No conversion
required.
0 Little-Endian
1
1
WORD
0 Little-Endian
BYTE
X
X
2
Reserve
Table 2-3: Data access of a S7-1500 controller
Standard block
Optimized block
1.
In the event of an unfavorable offset,
the controller needs 2x16 bit accesses
in order to be able to read a 4 byte
value (e.g. REAL value).
In addition the bytes have to be
changed.
The controller stores the tags, access
optimized. An access is performed with
32 bit (REAL).
A changing of the bytes is not
necessary.
2.
The complete byte is read and masked
per bit access.
The complete byte is blocked for any
other access.
Each bit is assigned a byte.
When accessing, the controller does not
have to mask the byte.
3.
Maximum block size is 64kB.
Maximum block size can be up to
16MB.
Programming Guideline for S7-1200/1500
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2 S7-1200/1500 Innovations
2.6 Optimized blocks
Recommendation
Always only use optimized blocks.
–
They do not require absolute addressing and can always be addressed
with symbolic data (object related). Indirect addressing is also possible with
symbolic data (see chapter 3.6.2 ARRAY data type and indirect field
accesses).
–
The processing of optimized blocks in the controller is much faster than
with standard blocks.
Avoid the copying/assigning of data between optimized and non-optimized
blocks. The required conversion between source and destination format
requires high processing time.
Example: Setting optimized block access
The block access is not reset automatically when a block is migrated from a
S7-300/400 controller to a S7-1200/1500. You can change the block access later
on to “optimized block access”. You need to recompile the program after changing
the block access. If you change the FBs to “optimized block access”, the assigned
instance data blocks are automatically updated.
Follow the instructions below, in order to set the optimized block access.
Table 2-4: Setting optimized block access
Step
Instruction
1.
Click the “Maximizes/minimizes the Overview” button in the project navigation.
2.
Navigate to “Program blocks“.
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The optimized block accesses for all newly created blocks for S7-1200/1500 is
enabled by default. Block access can be set for OBs, FBs and global DBs. For
instance DBs, the setting depends on the respective FB.
Programming Guideline for S7-1200/1500
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2.6 Optimized blocks
Step
3.
Instruction
This is where you see all blocks in the program and whether they are optimized
or not. In this overview the “Optimized block access” status can be conveniently
changed.
Note: Instance data blocks (here “Function_block_1_DB”) inherit the “optimized”
status from the respective FB. This is why the “optimized” setting can only be
changed on the FB. After the compilation of the project the DB accepts the
status depending on the respective FB.
Display of optimized and non-optimized blocks in the TIA Portal
For a global DB there are the same differences.
Figure 2-9: Optimized data block (without offset)
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In the two following figures the differences between an optimized and a nonoptimized instance DB can be seen.
Figure 2-10: Non-optimized data blocks (with offset)
Table 2-5: Difference: optimized and non-optimized data block
Optimized data block
Non-optimized data block
Optimized data blocks are addressed
symbolic. No “offset” is displayed.
At non-optimized blocks an “offset” is
displayed and can be used for addressing.
In optimized blocks every tag can be
declared with “Retain”.
In non-optimized blocks only all or no tags
can be declared with “Retain”.
Programming Guideline for S7-1200/1500
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2.6 Optimized blocks
The retentivity of tags of a global DB is defined directly in the global DB. The
default setting is non-retentive.
The retentivity of tags of one instance is defined in the function block (not in the
instance DB).These settings then apply to all instances of this FB.
Access types for optimized and non-optimized blocks
The following table displays all access types to blocks.
Table 2-6: Access types
Access type
Optimized block
Non-optimized
block
Symbolic
Indexed (fields)
Slice accesses
AT instruction
(Alternatively: slice access)
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Direct absolute
(Alternatively: ARRAY with
index)
Indirect absolute (pointer)
(Alternatively: VARIANT /
ARRAY with index)
Downloading without
reinitialization
Note
You will find further information in the following entries:
What differences should you watch out for between optimized data storage and
the standard type of block access in STEP 7 (TIA Portal) V12?
http://support.automation.siemens.com/WW/view/en/67655611
What properties do you have to pay attention to in STEP 7 V11 for the
instructions "READ_DBL" and "WRIT_DBL", when you are using DBs with
optimized access?
http://support.automation.siemens.com/WW/view/en/51434748
2.6.4
Conversion between optimized and non-optimized tags
The general recommendation is to work with optimized tags. However, if you want
to keep your previous programming in individual cases, this leads to a mixture of
optimized and non-optimized data storage in the program.
The system recognizes the internal storage of each tag, no matter if structured
(derived from a user-defined data type) or elementary (INT, LREAL, etc.).
In the case of type-identical allocations between two tags with different storage
locations, the system converts automatically. In the case of structured tags, this
conversion requires performance and should therefore be avoided, if possible.
Programming Guideline for S7-1200/1500
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2 S7-1200/1500 Innovations
2.6 Optimized blocks
2.6.5
Communication with optimized data
The interface (CPU, CM) transfers the data as they are arranged (no matter if
optimized or not).
Figure 2-11: CPU-CPU communication
Compatible
data transfer
(byte stream)
Send CPU
B1
32
39
Send data can be:
• optimized
• not optimized
• Tag (any type)
• Buffer (byte array)
4F
6D 7A
Receive CPU
…
FF
Receive data can be:
• optimized
• not optimized
• Tag (any type)
• Buffer (byte array)
Example
A tag with data type PLC (data record) is to be transferred to a CPU.
In the send CPU, the tag is interconnected as actual parameter with the
communication block (TSEND_C).
In the receive CPU, the receive data are assigned to a tag of the same type.
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0A
In this case, it is possible to symbolically continue to work directly with the
received data.
Note
Any tags or data blocks (derived from PLC data types) can be used as data
records.
Note
It is also possible that the send and receive data are not defined identically:
Send data
Receive data
optimized
-->
not optimized
not optimized
-->
optimized
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2.7 Block sizes
2.7
Block sizes
For S7-1200/1500 controllers the maximum size of blocks was significantly
increased in the main memory.
Table 2-7: Block sizes
Max. size and number
(regardless of the main memory
size)
S7 -300/400
S7-1200
S7-1500
Max. size
64 kB
64 kB
64 kB (non-optimized)
16 MB (optimized)
Max. number
16.000
59.999
59.999
Max. size
64 kB
64 kB
512 kB
Max. number
7.999
65.535
65.535
Max. number
4.096 (CPU319)
6.000 (CPU412)
1.024
6.000 (CPU1516)
DB
FC/FB
FC / FB / DB
Use the DBs for S7-1500 controllers as data container of very large data
volumes.
Data volumes of > 64 kB can be stored in an optimized DB (max. size 16 MB)
with S7-1500 controllers.
2.8
New data types for S7-1200/1500
S7-1200/1500 controllers support new data types in order to make programming
more convenient. With the new 64 bit data types considerably larger and more
accurate values can be used.
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Recommendation
Note
You will find further information in the following entry:
How is the conversion of data types performed in the TIA Portal for the
S7-1200/1500?
http://support.automation.siemens.com/WW/view/en/60546567
2.8.1
Elementary data types
Table 2-8: Integer data types
Type
Size
Value range
USint
8 bit
0 .. 255
SInt
8 bit
-128 .. 127
UInt
16 bit
0 .. 65535
UDInt
32 bit
0 .. 4.3 million
ULInt*
64 bit
0 .. 18.4 billion
LInt*
64 bit
-9.2 billion .. 9.2 billion
* only for S7-1500
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2.8 New data types for S7-1200/1500
Table 2-9: Floating-point decimal data types
Type
Size
Value range
Real
32 bit (1 bit signs, 8 bit exponent, 23 bit mantissa),
-3.40e+38 .. 3.40e+38
accurate to 7 decimal places
LReal
2.8.2
64 bit (1 bit signs, 11 bit exponent, 52 bit
mantissa), accurate to 15 decimal places
-1.79e+308 .. 1.79e+308
Date_Time_Long data type
Table 2-10: Structure of DTL (Date_Time_Long)
Year
Month
Day
Weekday
Hour
Minute
Second
Nanosecond
DTL always reads the current system time. Access to the individual values is
through the symbolic names (e.g. My_Timestamp.Hour)
Advantages
All partial areas (e.g. Year, Month, …) can be addressed symbolically.
Use the new DTL data type instead of LDT and address symbolically (e.g.
My_Timestamp.Hour).
Note
You will find further information in the following entries:
In STEP 7 (TIA Portal), how can you input, read out and edit the date and time
for the CPU modules of S7-300/S7-400/S7-1200/S7-1500?
http://support.automation.siemens.com/WW/view/en/58387452
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Recommendation
Which functions are available in STEP 7 V5.5 and in TIA Portal for processing
the data types DT and DTL?
http://support.automation.siemens.com/WW/view/en/63900230
2.8.3
VARIANT data type
A parameter of the VARIANT type is a pointer that can point to tags of different
data types. In contrast to the ANY pointer the VARIANT is a pointer with type test.
The target structure and source structure are checked at runtime and have to be
identical.
VARIANT is used, for example, as input for communication blocks (TSEND_C).
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2.8 New data types for S7-1200/1500
Figure 2-12: VARIANT data type as input parameter for the TSEND_C instruction
VARIANT
In this case includes the check of the
structure TCON_IP_v4
Advantages
Integrated type test
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Symbolic addressing for optimized blocks
Recommendation
Use the VARIANT data type instead of the ANY pointer. Due to the integrated
type test, errors are detected early on and due to the symbolic addressing the
program code can be easily interpreted.
As another alternative you can use the indexed ARRAYs for the ANY pointer
(see chapter 3.6.2 ARRAY data type and indirect field accesses).
Note
You will find further information in the following entry:
How can memory areas be copied in STEP 7 (TIA Portal)?
http://support.automation.siemens.com/WW/view/en/59886704
How do you program the "VARIANT" data type for indirect addressing for the S71200 in STEP 7 (TIA Portal) V11?
http://support.automation.siemens.com/WW/view/en/42603286
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2.9 Instructions
2.9
Instructions
2.9.1
CALCULATE
With the CALCULATE instruction you can carry out mathematical calculations (e.g.
(IN1 + IN2) * IN3) that are independent from the data type. The mathematical
formula is programmed in the formula editor of the instruction.
Figure 2-13: CALCULATE instruction with formula editor
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Note
For more information refer to the Online Help of the TIA Portal with the
“CALCULATE” instruction.
Advantages
A mathematical formula only needs one instruction
Time saving due to simple configuration
Properties
Supports bit sequences, integers, floating-point numbers
Supports numerous mathematical functions (all basic arithmetic operations,
trigonometric functions, rounding, logarithm, etc.)
Number of inputs is extendable
Recommendation
Always use the CALCULATE instruction for mathematical calculations instead
of many calls of instructions, such as, e.g. ADD, SUB, etc.
2.9.2
MOVE instructions
STEP 7 (TIA) provides the following MOVE instructions. The instruction
MOVE_BLK_VARIANT for S7-1200/1500 is new.
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2.9 Instructions
Table 2-11:Move instructions
Note
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Instruction
Usage
Properties
MOVE
Copy value
Copies the content of the parameter at
the IN input to the parameter of the
OUT output.
The parameters at the input and output
must be of the same data type.
The parameters can also be structured
tags (PLC data types).
MOVE_BLK
Copy array
Copies the content of an array to
another array.
The source and target array must be of
the same data type.
UMOVE_BLK
Copy array
without
interruption
Copies the content of an array without
any interruption to another array.
The source and target array must be of
the same data type.
MOVE_BLK_VARIANT
Copy array
Copies one or several structured tag(s)
(PLC data types).
Recognizes data types at runtime.
Supplies detailed error information.
Apart from the elementary and
structured data types, also PLC data
types, arrays, and array DBs are
supported
UMOVE_BLK: The copy process cannot be interrupted by another activity of the
operating system. Therefore, the alarm reaction times of the CPU might increase
during processing of the instruction "Copy array without interruption".
For the complete description of the MOVE instructions, please refer to the TIA
Portal Online Help.
2.9.3
RUNTIME
Using the "RUNTIME" instruction you measure the runtime of the complete
program, single blocks or the command sequences. You can call this instruction in
SCL (S7-1200/S7-1500) and in STL (S7-1500).
NOTE
You will find further information in the following entry:
With S7-1200/S7-1500, how do you measure the time of a program section or
the complete program cycle at runtime?
http://support.automation.siemens.com/WW/view/en/87668318
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2.10 Symbolic and comments
2.10
Symbolic and comments
Advantages
You can make the code easy to understand and readable for your colleagues with
the use of symbolic names and comments in your program.
The complete symbolic is saved together with the program code during the
download to the controller and allows fast maintenance of the plant when no offline
project is at hand.
Recommendation
Use the comments in the programs in order to improve readability. Network title
comments are visible even if networks are collapsed.
Design the program code in a way so that colleagues can understand the
program straight away.
In the following example you can see the extensive options for commenting the
program editors.
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Example
In the following figure you can see the options for commenting in the LAD editor
(same functionality in FDB).
Figure 2-14: Commenting in the user program (LAD)
1
2
3
4
The following comments are possible:
3. Block comment
4. Network title comment
5. Network comment
6. Comment on instructions, blocks and functions (open, close, etc.)
In the programming languages SCL and STL, it can be commented with // in every
row.
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2.11 System constants
Example
Filling level:= Radius * Radius * PI * height;
// calculation of the filling level for medium tank
2.11
System constants
For S7-300/400 controllers the identification of hardware and software components
is performed by logic address or diagnostic addresses.
For S7-1200/1500 the identification is by system constants. All hardware and
software components (e.g. interfaces, modules, OBs, ...) of the S7-1200/1500
controllers have their own system constants. The system constants are
automatically created during the setup of the device configuration for the central
and distributed I/O.
Advantages
You can address via module names instead of hardware identification.
Assign function-related module names in order to identify the modules easily
during programming.
Example
In the following example you can see how system constants are used in the user
program.
Figure 2-15: “System constants” in the user program
2
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Recommendation
1
3
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2.12 Internal reference ID for controller and HMI tags
1. System constants of a controller can be found in the “PLC tags –
Default tag table” folder.
2. The system constants are in a separate tab in the “Default tag table”.
3. In this example the symbolic name “Robot_arm_left” was assigned for a DI
module.
You can also find the module under this name in the system constant tab.
In the user program “Robot_arm_left” is interconnected with the “GET_DIAG”
diagnostic block.
Note
You will find further information in the following entry:
What meaning do the system constants have for the S7-1200/1500 in STEP 7
(TIA Portal)?
http://support.automation.siemens.com/WW/view/en/78782836
Siemens AG 2014 All rights reserved
2.12
Internal reference ID for controller and HMI tags
STEP 7, WinCC, Startdrive, Safety and others integrate into the joint data base of
the TIA Portal engineering framework. Changes of data are automatically accepted
in all the locations in the user program, independent from whether this happens in
a controller, a panel or a drive. Therefore no data inconsistencies can occur.
Copyright
If you create a tag, the TIA Portal automatically creates a unique reference ID. The
reference ID cannot be viewed or programmed by you. This procedure is internal
referencing. When changing tags (address), the reference ID remains unchanged.
In the figure below the internal reference to the data is displayed schematically.
Figure 2-16: Internal reference ID for PLC and HMI
PLC_1
HMI_1
PLC Symbol Absolute Internal PLC
name
address reference ID
NOTE
Internal HMI HMI Symbol
reference ID
name
Access
mode
Connection
with PLC
Motor_1
I0.0
000123
009876
Motor_1
<symbolic
access>
PLC_1
Valve_2
Q0.3
000138
000578
Valve_2
<symbolic
access>
PLC_1
The ID will be invalid if …
name is changed.
type is changed.
tag is deleted.
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2.13 STOP mode in the event of errors
Advantages
You can rewire tags without changing internal relations. The communication
between controller, HMI and drive also remains unchanged.
The length of the symbolic name does not have an influence on the
communication load between controller and HMI.
Properties
If you change addresses of PLC tags, you only have to reload the controller. It is
not necessary to reload the HMI devices, since internally, the system addresses
with the reference IDs (see Figure 2-17: Changing address or adding row).
Figure 2-17: Changing address or adding row
PLC Tags
%I0.0
Motor_1
Changing address
&
PLC
Motor_1
%I2.0
Adding row
&
PLC
2.13
STOP mode in the event of errors
In comparison to S7-300/400 there are fewer criteria with the S7-1200/1500 that
lead to the “STOP” mode.
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DB Elements
Due to the changed consistency check in the TIA Portal, the “STOP” mode for S71200/1500 controllers can already be excluded in advance in most cases. The
consistency of program blocks is already checked when compiling in the
TIA Portal. This approach makes the S7-1200/1500 controllers more fault tolerant
to errors than their predecessors.
Advantages
There are only three fault situations that put the S7-1200/1500 controllers into the
STOP mode. This makes the programming of the error management clearer and
easier.
Properties
Table 2-12: Responses to errors of S7-1200/1500
Error
S7-1200
S7-1500
1.
Cycle monitoring time
exceeded once
RUN
STOP, when OB80 is
not configured
2.
Cycle monitoring time
exceeded twice
STOP
STOP
3.
Programming errors
RUN
STOP, when OB121 is
not configured
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2.13 STOP mode in the event of errors
Error OBs:
OB80 “Time error interrupt” is called by the operating system when the
maximum cycle time of the controller is exceeded.
OB121 “Programming error” is called by the operating system when an error
occurs during program execution.
For every error, in addition, an entry is automatically created in the diagnostic
buffer.
Note
For S7-1200/1500 controllers there are other programmable error OBs
(diagnostic error, module rack failure, etc.).
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More information on error responses of S7-1200/1500 can be found in the online
help of the TIA Portal under “Events and OBs”.
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3 General Programming
3.1 Operating system and user program
3
General Programming
3.1
Operating system and user program
SIMATIC controllers consist of operating system and user program.
The operating system organizes all functions and sequences of the controller
that are not connected with a specific control task (e.g. handling of restart,
updating of process image, calling the user program, error handling, memory
management, etc.). The operating system is an integral part of the controller.
The user program includes all blocks that are required for the processing of
your specific automation task. The user program is programmed with program
blocks and loaded onto the controller.
Figure 3-1: Operating system and user program
User
program
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Hardware
Operating
system
OB
Main
cyclic
call
FB
FC
Local
FC
FC
Global
For SIMATIC controllers the user program is always executed cyclically. The
“Main” cycle OB already exists in the “Program blocks” folder after a controller was
created in STEP 7. The block is processed by the controller and recalled in an
infinite loop.
3.2
Program blocks
In STEP 7 (TIA Portal) there are all familiar block types from the previous STEP 7
versions:
Organization blocks
Function blocks
Functions
Data blocks
Experienced STEP 7 users will know their way around straight away and new
users can very easily get familiar with the programming.
Advantages
You can give your program a good and clear structure with the different block
types.
Due to a good and structured program you get many function units that can be
multiply reused within a project and also in other projects. These function units
then usually only differ by a different configuration (see chapter
3.2.8 Reusability of blocks).
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3.2 Program blocks
You project or your plant becomes more transparent. Error states in a plant
can be more easily detected, analyzed and removed. The maintainability of
your plant becomes easier. This is also the case for errors in programming.
Recommendation
Structure your automation task.
Divide the entire function of your plant into individual areas and form subfunction units. Divide these sub function units again into smaller units and
functions. Divide until you get functions that you can use several times with
different parameters.
Specify the interfaces between the function units. Define the unique interfaces
for functionalities that are to be delivered by “third party companies”.
All organization blocks, function blocks and functions can be programmed with the
following languages:
Table 3-1: Programming languages
Programming language
S7-1200
S7-1500
Ladder (LAD)
Function block diagram (FBD)
Graph
planned
Statement list (STL)
3.2.1
Organization blocks (OB)
Figure 3-2: “Add new block” dialog (OB)
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Structured control language (SCL)
OBs are the interface between the operating system and the user program. They
are called by the operating system and control, e.g. the following processes:
Startup behavior of the controller
Cyclic program processing
Interrupt-controlled program processing
Error handling
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3.2 Program blocks
Depending on the controller a number of different OB types are available.
Properties
OBs are called by the operating system of the controller
Several Main OBs can be created in a program. The OBs are processed
sequentially by OB number.
Figure 3-3: Using several Main OBs
User program
Main_1
OB1
Main_y
OB200
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Main_x
OB300
FB
FC
Local
FB
FC
Local
FB
FC
Local
Recommendation
Encapsulate the different program parts which should maybe be replaceable
from controller to controller, into several Main OBs.
Avoid the communication between the different Main OBs. They can then be
used independent from each other. If you nevertheless exchange data
between the individual main OBs, use the global DBs (see chapter 4.2 No bit
memory but global data blocks).
Divide all program parts that belong to each other into folders and store them
for reusability in the project or global library.
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3.2 Program blocks
Figure 3-4: Storing program parts in order in the project library
Note
You will find further information in the following entry:
Which organization blocks can be used in STEP 7 (TIA Portal)?
http://support.automation.siemens.com/WW/view/en/58235745
3.2.2
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For further information, please refer to chapter 3.7 Libraries.
Functions (FC)
Figure 3-5: “Add new block” dialog (FC)
FCs are blocks without cyclic data storages. This is why the values of block
parameters cannot be saved until the next call and has to be provided with actual
parameters when called.
Properties
FCs are blocks without cyclic data storages.
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3.2 Program blocks
Temporary and out tags are undefined when called in non-optimized blocks. In
optimized blocks, the values are always preset to the default value (S7-1500
and S7-1200 Firmware V4). Thus, the resulting behavior is not accidental but
reproducible.
In order to permanently save the data of an FC, the functions of the global data
blocks are available.
FCs can have several outputs.
The function value can be directly reused in SCL in a formula.
Recommendation
Use the functions for continuously recurring applications that are called several
times in different locations of the user program.
Use the option to directly reuse the function value in SCL.
<Operand> := <FC name> (parameter list);
Example
Table 3-2: Reusing function value
Step
1.
Instruction
Create an FC with the mathematical formula (circular segment) and define the
“Return” value as the result for the formula.
FC
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In the following example a mathematical formula is programmed in a FC. The result
of the calculation is directly declared as return value and the function value can be
directly reused.
2.
Call the FC with the circular segment calculation in any block (SCL).
<Operand> := <FC name> (parameter list);
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3.2 Program blocks
3.2.3
Function blocks (FB)
Figure 3-6: “Add new block” dialog (FB)
FBs are blocks with cyclic data storage, in which values are permanently stored.
The cyclic data storage is realized in an instance DB.
Siemens AG 2014 All rights reserved
Figure 3-7: Calling a function block
Instance DB
Copyright
Call of a function block in the
block editor
Properties
FBs are blocks with cyclic data storage.
Temporary and out tags are undefined when called in non-optimized blocks. In
optimized blocks, the values are always preset to the default value (S7-1500
and S7-1200 Firmware V4). Thus, the resulting behavior is not accidental but
reproducible.
Static tags keep the value from cycle to cycle
Recommendation
Use the function blocks in order to create subprograms and structure the user
program. A function block can also be called several times in different locations
of the user program. This makes programming of frequently recurring program
parts easier.
If function blocks are applied multiply in the user program, use separate
instances, preferably multi-instances.
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3.2 Program blocks
3.2.4
Instances
The call of a function block is called instance. The data with which the instance is
working is saved in an instance DB.
Instance DBs are always created according to the specifications in the FB interface
and can therefore not be changed in the instance DB.
Figure 3-8: Structure of the interfaces of an FB
Instance
Input
Output
InOut
The instance DB consists of a permanent memory with the interfaces input, output,
InOut and static. In a volatile memory (L stack) temporary tags are stored. The
L stack is always only valid for one cycle. I.e. temporary tags have to be initialized
in each cycle.
Properties
Instance DBs are always assigned to a FB.
Instance DBs do not have to be created manually in the TIA Portal and are
created automatically when calling an FB.
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Static
The structure of the instance DB is specified in the appropriate FB and can
only be changed there.
Recommendation
Program it in a way so that the data of the instance DB can only be changed by
the appropriate FB. This is how you can guarantee that the block can be used
universally in all kinds of projects.
For further information, please refer to chapter 3.4 Block interfaces as data
exchange.
3.2.5
Multi-instances
With multi-instances called function blocks can store their data in the instance data
block of the called function block. I.e. if another function block is called in a function
block, it saves its data in the instance DB of the higher-level FBs. The functionality
of the called block is thus maintained even if it is transferred.
The following figure shows an FB that uses another FB (“IEC Timer”). All data is
saved in a multi instance DB. It is thus possible to create a block with an
independent time behavior, for example, a clock generator.
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3.2 Program blocks
Figure 3-9: Multi-instances
FB
Multi-instance DB
Switch-on
delay call
FB Parameter
FB Statics
TOF_TIME
Advantages
Reusability
Multiple calls are possible
Simple copying of programs
Good options for structuring during programming
Properties
Multi-instances are memory areas within instance DBs.
Recommendation
Use multi-instances in order to …
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Clearer program with fewer instance DBs
reduce the number of instance DBs.
create reusable and clear user programs.
program local functions e.g. timer, counter, edge detection.
Example
If you require the time and counter function, use the “IEC Timer” blocks and the
“IEC Counter” blocks instead of the absolutely addressed SIMATIC Timer. If
possible, also always use multi-instances here. This keeps the number of blocks in
the user program low.
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3 General Programming
3.2 Program blocks
Figure 3-10: Library of the IEC Timer
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Note
You will find further information in the following entry:
How do you declare the timers and counters for the S7-1500 in STEP 7
(TIA Portal) V12?
http://support.automation.siemens.com/WW/view/en/67585220
3.2.6
Global data blocks (DB)
Figure 3-11: “Add new block” dialog (DB
Variable data is located in data blocks that are available to the entire user program.
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3 General Programming
3.2 Program blocks
Figure 3-12: Global DB as central data memory
FC
OB
DB
FB
Local
Advantages
Well structured memory area
High access speed
Properties
All blocks in the user program can access global DBs.
Global DBs are either created via the program editor or according to a
previously created “user-defined PLC data type" (see chapter 3.6.3 STRUCT
data type and PLC data types).
Recommendation
Use the global DBs when data is used in different program parts or blocks.
Note
You will find further information in the following entry:
What access types, value columns and operating options are there for the global
data blocks in STEP 7 V12?
http://support.automation.siemens.com/WW/view/en/68015631
Copyright
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The structure of the global DBs can be arbitrarily made up of all data types.
3.2.7
Downloading without reinitialization
In order to change user programs that already run in a controller, S7-1200
(firmware V4.0) and S7-1500 controllers offer the option to expand the interfaces of
optimized function or data blocks during operation. You can load the changed
blocks without setting the controller to STOP and without influencing the actual
values of already loaded tags.
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3 General Programming
3.2 Program blocks
Figure 3-13: Downloading without reinitialization
Block
in project
Block in
the controller
Name
Name
Tag1
Tag1
3.4
Tag2
451
Tag3
23
Tag4
Tag4
0
Tag5
Tag5
0
Name
Value
Tag1
3.4
Tag2
451
Tag2
Tag3
23
Tag3
1
Block in
the controller
3
Value
2
Execute the following steps whilst the controller is in RUN mode.
1. Enable “Downloading without reinitialization”
2. Insert new defined tags in existing block
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3. Load block into controller
Advantages
Reloading of new defined tags without interrupting the running process. The
controller stays in “RUN” mode.
Properties
Downloading without reinitialization is only possible for optimized blocks.
New defined tags will be initialized. The remaining tags keep their current
values.
A block with reserve requires more memory space in the controller.
The memory reserve depends on the work memory of the controller; however it
is max. 2 MB.
It is assumed that a memory reserve has been defined for block.
By default the memory reserve is set to 100 byte.
The memory reserve is defined individually for every block.
The blocks can be variably expanded.
Recommendation
Define a memory reserve for blocks that are to be expanded during
commissioning (e.g. test blocks). The commissioning process is not interrupted
by download of new defined tags. The current values of already existing
variables are kept.
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3.2 Program blocks
Example: Setting memory reserve in block
The following table describes how you can set the memory reserve for the
downloading without reinitializing.
Table 3-3: Setting memory reserve
Step
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1.
Instruction
Right-click any optimized block in the project navigator and select “Properties”.
2.
Copyright
2
1
3
1.
2.
3.
Note
Click “Download without reinitialization”.
Enter the desired memory reserve for “Memory reserve”.
Confirm with "OK".
You can also set a default value for the size of the memory reserve for new
blocks in the TIA portal.
In the menu bar, navigate to "Options – Settings" and then to "PLC programming
– General – Download without reinitialization“.
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3.2 Program blocks
Example: Downloading without reinitialization
In the following example it is displayed how to download without reinitialization.
Table 3-4 Downloading without reinitialization
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Step
Note
Instruction
1.
Requirement: a memory reserve has to be set (see above)
2.
Open, e.g. an optimized global DB.
3.
Click the “Download without reinitialization” button and confirm the dialog with
“OK”
4.
Add a new tag (retentive tags are also possible).
5.
Download the block to the controller.
6.
Result:
Actual values of the block remain
Further information can be found in the online help of the TIA Portal under
“Loading block extensions without reinitialization”.
You will find further information in the following entry:
What options does the S7-1500 provide for downloading data in RUN?
http://support.automation.siemens.com/WW/view/en/76278126
3.2.8
Reusability of blocks
The block concept offers you a number of options to program in a structured and
effective way.
Advantages
Blocks can be used universally in any location of the user program.
Blocks can be used universally in different projects.
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3.3 Block interface types
When every block receives an independent task, a clear and well-structured
user program is automatically created.
There are clearly fewer sources of errors
Simple error diagnostic possible.
Recommendation
If you want to reuse the block, please note the following recommendations:
Always look at blocks as encapsulated functions. I.e. each block represents a
completed partial task within of the entire user program.
Use several cyclic Main OBs to group the plant parts.
Always execute a data exchange between the blocks via its interfaces and not
via its instances (see chapter 3.4.1 Block interfaces as data exchange).
Do not use project-specific data and avoid the following block contents:
Access to global DBs and use of individual instance DBs
–
Access to tags
–
Access to global constants
Reusable blocks have the same requirements as know-how-protected blocks
in libraries. This is why you have to check the blocks for reusability based on
the “Block can be used as know-how protected library element” block property.
Compile the block before the check.
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Copyright
–
Figure 3-14: Block attributes
3.3
Block interface types
FBs and FCs have three different interface types: In, InOut and Out. Via these
interface types the blocks are provided with parameters. The parameters are
processed and output again in the block. There are two different options for this
parameter transfer.
3.3.1
Call-by-value with In interface type
When calling the block, the value of the actual parameter is copied onto the input
parameter of the block for the In interface type. For this, additional memory is
required.
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3.4 Storage concept
Figure 3-15: Copying of the value to the input parameter
„My_int“
value: 31
FC / FB
IN
value: 31
Properties
Each block displays the same behavior with connected parameters
Values are copied when calling the block
3.3.2
Call-by-reference with InOut interface type
Figure 3-16: Referencing the value (pointer to data storage of the parameter)
"My_string"
value: 'test'
FC / FB
IN/OUT
Reference to "My_string"
Properties
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When calling the block the address of the actual parameter of the Input parameter
is referenced for the InOut interface type. For this, no additional memory is
required.
Each block displays the same behavior with connected parameters
Actual parameters are referenced with the block call
Recommendation
Generally use the InOut interface type for structured tags (e.g. of the ARRAY,
STRUCT, STRING, type…) in order to avoid enlarging the required data
memory unnecessarily.
3.4
Storage concept
For STEP 7 there is generally the difference between the global and local memory
area. The global memory area is available for each block in the user program. The
local memory area is only available within the respective block.
3.4.1
Block interfaces as data exchange
If you are encapsulating the functions and program the data exchange between the
blocks only via the interfaces, you will clearly have advantages.
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3.4 Storage concept
Advantages
Program can be made up modularly from ready blocks with partial tasks.
Program is easy to expand and maintain.
Program code is easier to read since there are no hidden cross accesses.
Recommendation
If possible, only use the local tags. This is how the blocks can be used
universally and modularly.
Use the data exchange via the block interfaces (In, Out, InOut), to ensure the
reusability of blocks.
Only use the instance data blocks as local memory for the respective function
block. Other blocks shall not be written into instance data blocks.
Figure 3-17: Avoiding accesses to instance data blocks
FB
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Local
OB
FC
FB
Local
If only the block interfaces are used for the data exchange it can be ensured that
all blocks can be used independent from each other.
Copyright
Figure 3-18: Block interfaces for data exchange
OB
FC
FB
Local
FB
Local
3.4.2
Global memory
Memories are called global when they can be accessed from any location of the
user program. There are hardware-dependent memories (e.g. bit memory, timers,
counters, etc.) and global DBs. For hardware-dependent memory areas there is the
danger that the program may not be portable to any controller because the areas
there may already be used. This is why you should use global DBs instead of
hardware-dependent memory areas.
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3.4 Storage concept
Advantages
User programs can be used universally and independent from the hardware.
The user program can be structured modularly without dividing bit memory
address areas for different users.
Optimized global DBs are clearly more powerful than the bit memory address
area that is not optimized for reasons of compatibility.
Recommendation
Do not use any bit memory and use global DBs instead.
Avoid hardware-dependent memory, such as, for example, clock memory or
counter. Use the IEC counter and timer in connection with multi-instances
instead (see chapter 3.2.5 Multi-instances). The IEC timers can be found under
“Instructions – Basic Instructions – Timer operations”.
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Figure 3-19: IEC Timers
3.4.3
Local memory
Static tags
Temporary tags
Recommendation
Use the static tags for values that are required for the next cycle.
Use the temporary tags as cache memory in current cycle. The access time for
temporary tags is shorter than for static ones.
Note
Optimized blocks: Temporary tags are initialized in any block call with the
“default value” (S7-1500 und S7-1200 Firmware V4).
Non-optimized blocks: Temporary tags are undefined for each call of the block.
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3.4 Storage concept
3.4.4
Access speed of memory areas
STEP 7 offers different options of memory accesses. For system-related reasons
there are faster and slower accesses to different memory areas.
Figure 3-20: Different memory accesses
Access speed
Non-structured
elementary data type FC
parameter
fast
1
intermediate
Retentive tags
slow
2
Non-retain tags
1
Temporary tags
1
4
5
Accesses to checks for at
runtime require
(register, indirect and
indirect DB accesses)
5
5
6
Copying between optimized
and non-optimized blocks
2
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Indexed accesses with
runtime tindex
3
Access to optimized DBs
Access to non-optimized
blocks
Fastest accesses in the S7-1200/1500 in descending order
1. Optimized blocks: Temporary tags, parameters of an FC and FB, non-retentive
static tags
2. Optimized blocks whose accesses for compiling are known:
–
Retentive FB tags
–
Optimized global DBs
3. Access to non-optimized blocks
4. Indexed accesses with index that was calculated at runtime (e.g. Motor [i])
5. Accesses that require checks at runtime
–
Accesses to DBs that are created at runtime or which were opened
indirectly (e.g. OPN DB[i])
–
Register access or indirect memory access
6. Copying of structures between optimized and non-optimized blocks (apart from
Array of Bytes)
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3.5 Retentivity
3.5
Retentivity
In the event of a failure of the power supply, the controller copies the retentive data
with its buffer energy from the controller’s work memory to a non-volatile memory.
After restarting the controller, the program processing is resumed with the retentive
data. Depending on the controller, the data volume for retentivity has different
sizes.
Controller
Usable retentive memory for bit memory,
times, counters, DBs and technology
objects
CPU 1211C
10 Kbytes
CPU 1212C
10 Kbytes
CPU 1214C
10 Kbytes
CPU 1215C
10 Kbytes
CPU 1511-1 PN
88 Kbytes
CPU 1513-1 PN
88 Kbytes
CPU 1516-3 PN/DP
472 Kbytes
Table 3-6: Differences of S7-1200 and S7-1500
S7-1200
Retentivity can only be set for bit memory
S7-1500
Retentivity can be set for bit memory, times
and counters
Advantages
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Table 3-5: Retentive memory for S7-1200/1500
Retentive data maintain their value when the controller goes to STOP and back
to RUN or in the event of a power failure and a restart of the controller.
Properties
For elementary tags of an optimized DB the retentivity can be set separately. Nonoptimized data blocks can only be defined completely retentive or non-retentive.
The retentive data can be deleted with the actions "memory reset" or "Reset to
factory settings" via:
Operating switch on the controller (MRES)
Display of the controller
Online via STEP 7 (TIA Portal)
Recommendation
Avoid the setting “Set in IDB”. Always set the retentive data in the function
block and not in the instance data block.
The “Set in IDB” setting increases the processing time of the program
sequence. Always either select “Non-retain” or “Retain” for the interfaces in the
FB.
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3.5 Retentivity
Figure 3-21: Program editor (Functions block interfaces)
Example: Retentive of PLC tags
The setting of the retentive data is performed in the tables of the PLC tags, function
blocks and data blocks.
Figure 3-23: Setting of the retentive tags in the table of PLC tags
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Figure 3-22: Program editor (Data block)
Retentivity can be set from
address 0 onward!
e.g. from MB0, T0 or C0
Example: Retentive counter
You can also declare instances of functions (timer, counter, etc.) retentive. As
already described in chapter 3.2.5 Multi-instances
.
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3.6 Symbolic addressing
Figure 3-24: Retentive counter as multi-instance
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NOTE
If the retentive memory on the PLC is not sufficient, it is possible to store data in
the form of data blocks that are only located in the load memory of the PLC. The
following entry is described by taking the example of an S7-1200. This
programming also works for S7-1500.
You will find further information in the following entry:
In STEP 7 V11, how do you configure data blocks with the "Only store in load
memory" attribute for an S7-1200?
http://support.automation.siemens.com/WW/view/en/53034113
3.6
Symbolic addressing
3.6.1
Symbolic instead of absolute addressing
The TIA Portal is optimized for symbolic programming. This results in many
advantages. Due to the symbolic addressing you can program without having to
pay attention to the internal data storage. The controller handles where the best
possible storage is for the data. You can therefore completely concentrate on the
solution for your application task.
Advantages
Easier to read programs through symbolic tag names
Automatic update of tag names at all usage locations in the user program
Memory storage of the program data does not have to be manually managed
(absolute addressing)
Powerful data access
No manual optimization for performance or program size reasons required
IntelliSense for fast symbol input
Fewer program errors due to type checking (validity of data types is checked
for all accesses)
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3.6 Symbolic addressing
Recommendation
“Don’t bother about the organization of the data storage“
“Think” symbolically. Enter the “descriptive” name for each function, tag or
data, such as, for example, Pump_boiler_1, heater_room_4, etc. This is how a
generated program can easily be read without requiring many comments.
Give all the tags used a direct symbolic name and define it afterwards with a
right-click.
Example
Table 3-7: Example for creating symbolic tags
Step
Instruction
Open the program editor and open any block.
2.
Enter a symbolic name directly at the input of an instruction.
3.
Right-click next to the block and select “Define tag…” in the context menu.
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1.
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3.6 Symbolic addressing
Step
4.
Instruction
Define the tag.
There is an elegant method to save time, if you want to define several tags in a
network. Assign all tag names first of all. Then define all tags at the same time with
the dialog of step 4.
Copyright
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Note
You will find further information in the following entry:
Why is universal definition and utilization of symbols in STEP 7 (TIA Portal) V12
obligatory for the S7-1500?
http://support.automation.siemens.com/WW/view/en/67598995
3.6.2
ARRAY data type and indirect field accesses
The ARRAY data type represents a data structure that consists of several elements
of the same data type. The ARRAY data type is suitable, for example, for the
storage of recipes, material tracking in a queue, cyclic process acquisition,
protocols, etc.
Figure 3-25: ARRAY with 10 elements of the Integer (INT) data type
You can indirectly access individual elements in the ARRAY with a runtime tag
(array [“index”]).
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3.6 Symbolic addressing
Figure 3-26: Indirect field access
LAD / FBD:
SCL:
Advantages
Simple access since the data type of the ARRAY elements is irrelevant for the
access.
Fast creation and expansion possible
Useable in all programming languages
Properties
Structured data type
Data structure made of fixed number of elements of the same data type
ARRAYs can be created also multi-dimensional
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No complicated pointer creation required
Possible indirect access with runtime tag with dynamic index calculation at
runtime
Recommendation
Use ARRAY for indexed accesses instead of pointer (e.g. ANY pointer). This
makes it easier to read the program since an ARRAY is more meaningful with
a symbolic name than a pointer in a memory area.
As run tag use the INT data type as temporary tag for highest performance.
Use the “MOVE_BLK” instruction to copy parts of an ARRAY into another one.
Use the “GET_ERR_ID” instruction to catch access errors within the Array.
Note
You will find further information in the following entry:
How do you implement an array access with an S7-1500 with variable index?
http://support.automation.siemens.com/WW/view/en/67598676
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3.6 Symbolic addressing
3.6.3
STRUCT data type and PLC data types
The STRUCT data type represents a data structure which is made up of elements
of different data types. The declaration of a structure is performed in the respective
block.
Figure 3-27: Structure with elements with different data types
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In comparison to structures, PLC data types are defined across the controller in the
TIA Portal and can be centrally changed. All usage locations are automatically
updated.
PLC data types are declared in the “PLC data types” folder in the project navigation
before being used.
Copyright
Figure 3-28: PLC data types
Advantages
A change in a PLC data type is automatically updated in all usage locations in
the user program.
Recommendation
Use the PLC data types to summarize several associated data, such as, e.g.
frames or motor data (setpoint, speed, rotational direction, temperature, etc.)
Always use PLC data types instead of structures for the multiple uses in the
user program.
Use the PLC data types for structuring into data blocks.
Use the PLC data types in order to specify a structure for a data block. The
PLC data type can be used for any number of DBs. You can easily and
conveniently create as many DBs of the same structure and adjust them
centrally on the PLC data type.
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3.6 Symbolic addressing
Note
You will find further information in the following entries:
How do you initialize structures into optimized memory areas for the S7-1500
STEP 7 (TIA Portal)?
http://support.automation.siemens.com/WW/view/en/78678761
How do you create a PLC data type for an S7-1500 controller?
http://support.automation.siemens.com/WW/view/en/67599090
In STEP 7 (TIA Portal) V12, how do you apply your own data types (UDT)?
http://support.automation.siemens.com/WW/view/en/67582844
Why should whole structures instead of many single components be transferred
for the S7-1500 when a block is called?
http://support.automation.siemens.com/WW/view/en/67585079
Copyright
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3.6.4
Access to I/O areas with PLC data types
With S7-1500 controllers, you can create PLC data types and use them for
structured access to inputs and outputs.
Figure 3-29: Access to I/O areas with PLC data types
1
PLC data type
PLC tag
2
FB call
FB interface
3
4
1. PLC data type with all required data
2. PLC tag of the type of the created PLC data type and start address of the I/O
data area (%Ix.0 or %Qx.0, e.g., %I0.0, %Q12.0, …)
3. Transfer of the PLC tag as actual parameter to the function block
4. Input of the function block is of the type of the created PLC data type
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Advantages
High programming efficiency
Easy multiple usability thanks to PLC data types
Recommendation
Use PLC data types for access to I/O areas, for example, to symbolically
receive and send drive telegrams.
3.6.5
Slice access
For S7-1200/1500 controllers, you can access the memory area of tags of the Byte,
Word, DWord or LWord data type. The division of a memory area (e.g. byte or
word) into a smaller memory area (e.g. Bool) is also called slice. In the figure below
displays the symbolic bit, byte and word accesses to the operands.
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Figure 3-30: Slice access
Advantages
High programming efficiency
No additional definition in the tag declaration required
Simple access (e.g. control bits)
Recommendation
Use the slice access rather than AT construct via accessing certain data areas
in operands.
Note
You will find further information in the following entry:
How in STEP 7 (TIA Portal) can you access the unstructured data types bit-bybit, byte-by-byte or word-by-word and symbolically?
http://support.automation.siemens.com/WW/view/en/57374718
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3.7 Libraries
3.7
Libraries
With the TIA Portal you can create independent libraries from different project
elements that can be easily reused.
Advantages
Simple storage for the data configured in the TIA Portal:
–
Complete devices (controller, HMI, drive, etc.)
–
Controller programs, blocks, tags, monitoring tables
–
HMI image, HMI tags, scripts, etc.
Cross-project exchange via libraries
Central update function of library elements
Versioning library elements
Recommendations
Create the master copies for easy reusability of blocks, hardware
configurations, HMI images, etc.
Create the types for the system-supported reusability of library elements:
–
Versioning of blocks
–
Central update function of all usage locations
Use the global library for the exchange with other users or as central storage
for the simultaneous use of several users.
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Fewer error sources when using control blocks through system-supported
consideration of dependencies
3.7.1
Types of libraries and library elements
Generally there are two different types of libraries:
"Project library"
"Global library".
The content consists of two storage types each:
"Types"
"Master Copies"
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3.7 Libraries
Figure 3-31: Libraries in the TIA Portal
1
3
4
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2
(1) "Project library"
–
Integrated in the project and managed with the project
–
Allows the reusability within the project
(2) "Global library"
–
Independent library
–
Use within several projects possible
A library includes two different types of storage of library elements:
(3) "Master copies"
–
Copy of configuration elements in the library (e.g. blocks, hardware, PLC
tag tables, etc.)
–
Copies are not connected with the elements in the project.
–
Master copies can also be made up several configuration elements.
(4) "Types"
–
Types are connected with your usage locations in the project. When types
are changed, the usage locations in the project can be updated
automatically.
–
Supported types are controller blocks (FCs, FBs), PLC data types, HMI
images, HMI faceplates, HMI UDT, scripts).
–
Subordinate elements are automatically typified.
–
Types are versioned: Changes can be made by creating a newer version.
–
There can only be one version of a used type within a controller.
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3.7 Libraries
3.7.2
Type concept
The type concept allows the creation of standardized automation functions that you
can use in several plants or machines. The type concept supports you with
versioning and updating functions.
You can use types from the library in the user program. This offers the following
advantages:
Advantages
Central update of all usage locations in the project
Unwanted modifications of usage locations of types are not possible.
The system guarantees that types always remain consistent by hindering
unwanted delete operations.
If a type is deleted, all usage locations in the user program are deleted.
Properties
By using types you can make the changes centrally and update them in the
complete project.
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Figure 3-32: Typifying with user libraries
Project
User library
Use
without
typification
Master copy
Use
Use
Central update to
newer version
Update
Use V2
Typ V1
with typification
Copyright
Use V2
Typ V2
Use V2
Types are always marked in the project for better identification
3.7.3
Differences for typifiable objects for controller and HMI
There are system-related differences between the typifiable objects for controllers
and HMI:
Table 3-8: Differences of types for controller and HMI
Controller
HMI
Subordinate control elements are typified.
Subordinate HMI elements are not typified.
Subordinate control elements are
instanced.
Subordinate HMI elements are not
instanced.
Control elements are edited in a test
environment.
HMI images and HMI scripts are edited in a
test environment. Faceplates and HMI UDTs are directly edited in the library
without test environment.
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3.7 Libraries
Further information on the handling of libraries can be found in the following
example.
3.7.4
Versioning of a block
Example: Creating a type
The following example shows you how the basic functions of the libraries are used
with types.
Table 3-9: Creating a type
Instruction
1.
Create a new PLC data type with “Add new data type” and create some tags.
Later on this is the subordinate type.
2.
Create a new function block with “Add new Block”. This is the higher-level type.
3.
Define an input tag of the data type you have created. The PLC data type is
therefore subordinate to the function block.
4.
Drag the function block via drag & drop into the “Types” folder in the project
library.
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Step
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3.7 Libraries
Step
Instruction
Optionally assign: Type name, version, author and comment and confirm the
dialog with “OK”.
6.
The subordinate PLC data type is automatically also stored in the library.
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5.
Example: Changing a type
Table 3-10: Changing a type
Step
1.
Instruction
Right-click the block in the “Project library” and select “Edit type”
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3.7 Libraries
Step
2.
Instruction
Select which controller is to be used as test environment and confirm the dialog
with “OK”.
3.
The library view opens. A new version of the block has been created and is now
marked with “in test”.
4.
Add another input tag.
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If several controllers in the project use the selected block, a controller has to be
selected as test environment.
In this place you have the option to test the change on the block by loading the
project onto a controller. When you have finished testing the block, continue with
the following steps.
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3.7 Libraries
Step
Instruction
Click the “Release version” button.
6.
A dialog box opens. Here you can store a version-related comment. Confirm the
dialog with “OK”.
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5.
Copyright
If there are several usage locations of the block in different controllers of the
project, you can update them all at the same time: “Update instances in the
project”.
If older versions of the element are no longer required you can delete them by
clicking “Delete unused type versions from library”
7.
Close the library view with “Close library view”
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3 General Programming
3.8 Process interrupts
3.8
Process interrupts
The processing of the user program can be influenced by events such as process
interrupts. When you need a fast response of the controller to hardware events
(e.g. a rising edge of a channel of a digital input module), configure a process
interrupt. For each process interrupt a separate OB can be programmed. This OB
is called by the operating system of the controller in the event of a process
interrupt. The cycle of the controller is therefore interrupted and continued after
processing the process interrupt.
Figure 3-33: Process interrupt is calling OB
Event
e.g. falling
edge E6.1
e.g. rising
edge E0.0
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Hardware
interrupt
OB40
Hardware
interrupt_1
OBxxx
In the following figure you can see the configuration of a “hardware interrupt” in the
hardware configuration of a digital input module.
Copyright
Figure 3-34: Configuring hardware interrupt
Advantages
Fast system response to events (rising, falling edge, etc.)
Each event can start a separate OB.
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3 General Programming
3.8 Process interrupts
Recommendation
Use the process interrupts in order to program fast responses to hardware
events.
If the system responses are not fast enough despite programming a process
interrupt, you can still accelerate the responses. Set as small an “Input delay”
as possible in the module. A response to an event can always only occur if the
input delay has lapsed. The input delay is used for filtering the input signal in
order to, for example, compensate faults such as contact bounce or chatter.
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Figure 3-35: Setting input delay
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3 General Programming
3.9 Other performance recommendations
3.9
Other performance recommendations
Here you can find some general recommendations that enable faster program
processing of the controller.
Recommendation
Note the following recommendations for programming S7-1200/1500 controllers in
order to achieve a high performance:
LAD/FBD: Disable “generate ENO” for blocks. This avoids tests at runtime.
STL: Do not use registers since address and data registers are only emulated
for compatibility reasons by S7-1500.
Note
You will find further information in the following entry:
Copyright
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How do you disable the ENO enable output of an instruction?
http://support.automation.siemens.com/WW/view/en/67797146
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3 General Programming
3.10 SCL programming language: Tips and tricks
3.10
SCL programming language: Tips and tricks
3.10.1
Using call templates
Many instructions of the programming languages offer a call template with a list of
existing formal parameters.
Example
Table 3-11: Easy expanding of the call template
Instruction
1.
Drag an instruction from the library into the SCL program. The editor shows the
complete call template.
2.
Now fill in the required parameter and finish the entry with the “Return” button.
3.
The editor automatically reduces the call template.
4.
If you want to edit the complete call later on again, proceed as follows.
Click into the call at any place and then click “CTRL+SHIFT+SPACE”. You are
now in the Call Template mode. The editor expands the call again. You can
navigate with the “TAB” button through the parameters.
5.
Note: In the “Call Template” mode the writing is in italics.
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Step
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3 General Programming
3.10 SCL programming language: Tips and tricks
3.10.2
What instruction parameters are mandatory?
If you are expanding the call template, the color coding will show you straight away
what formal parameters of an instruction are optional and which ones are not.
Mandatory parameters are marked dark.
3.10.3
Drag & drop with entire tag names
In the SCL editor you can also use drag & drop functions. For tag names you are
additionally supported. If you want to replace one tag for another, proceed as
follows.
Table 3-12: Drag & drop with tags in SCL
Step
Drag the tag via drag & drop to the tag in the program that is to be replaced.
Hold the tag for more than 1 second before releasing it.
> hold for 1 second
The complete tag is replaced.
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1.
Instruction
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3 General Programming
3.10 SCL programming language: Tips and tricks
3.10.4
Efficiently inserting CASE instruction
With the CASE instruction in SCL, it will be exactly jumped to the selected CASE
block condition. After executing the CASE block the instruction is finished. This
allows you, for example, to check frequently required value ranges more
specifically and easily.
Example
CASE #myVar OF
5:
FC5(#myParam);
10,12:
FC10(#myParam);
15:
FC15(#myParam);
0..20:
FCGlobal(#myParam);
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// FCGlobal is never called for the values 5, 10, 12 or 15!
ELSE
END_CASE;
3.10.5
No manipulation of loop counters for FOR loop
FOR loops in SCL are pure counter loops, i.e. the number of iterations is fixed
when the loop is entered. In a FOR loop, the loop counter cannot be changed.
With the EXIT instruction a loop can be interrupted at any time.
Advantages
The compiler can optimize the program better, since it does not know the
number of iterations.
Example
FOR #var := #lower TO #upper DO
#var := #var + 1; // no effect, Compiler -> Warning
END_FOR;
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3 General Programming
3.10 SCL programming language: Tips and tricks
3.10.6
FOR loop backwards
In SCL you can also increment the index of FOR loops backwards or in another
step width. For this, use the optional “BY” key word in the loop head.
Example
FOR #var := #upper TO #lower BY -2 DO
END_FOR;
If you are defining “BY” as “-2”, as in the example, the counter is lowered by 2 in
every iteration. If you omit “BY”, the default setting for “BY” is 1
3.10.7
Simple creating of instances for calls
Example
Table 3-13: Easy creation of instances
Step
Instruction
1.
Give the block name a: followed by a "." (dot). The automatic compilation now
shows you the following.
2.
On the top you can see the already existing instances. In addition, you can
directly create a new single instance or multi-instance.
Use the shortcuts "s" or "m" to go directly to the respective entries in the
automatic compilation window.
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If you prefer to work with the keyboard, there is a simple possibility to create
instances for blocks in SCL.
3.10.8
Handling of time tags
You can calculate the time tags in SCL just as with normal numbers i.e. you do not
need to look for additional functions, such as, e.g. T_COMBINE but you can use
simple arithmetic. This approach is called “overload of operands”. The SCL
compiler automatically uses the suitable functions. You can use a reasonable
arithmetic for the time types and can therefore program more efficiently.
Example
TimeDifference := TimeStamp_1 – TimeStamp_2;
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3 General Programming
3.10 SCL programming language: Tips and tricks
The following table summarizes the overloaded operators and which operation is
behind it:
Table 3-14: Overloaded operands for SCL
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Overloaded operand
Operation
ltime + time
T_ADD LTime
ltime + time
T_SUB LTime
ltime + lint
T_ADD LTime
ltime + lint
T_SUB LTime
time + time
T_ADD Time
time + time
T_SUB Time
time + dint
T_ADD Time
time + dint
T_SUB Time
ldt + ltime
T_ADD LDT / LTime
ldt + ltime
T_ADD LDT / LTime
ldt + time
T_ADD LDT / Time
ldt + time
T_SUB LDT / Time
dtl + ltime
T_ADD DTL / LTime
dtl + ltime
T_SUB DTL / LTime
dtl + time
T_ADD DTL / Time
dtl + time
T_SUB DTL / Time
ltod + ltime
T_ADD LTOD / LTime
ltod + ltime
T_SUB LTOD / LTime
ltod + lint
T_ADD LTOD / LTime
ltod + lint
T_SUB LTOD / LTime
ltod + time
T_ADD LTOD / Time
ltod + time
T_SUB LTOD / Time
tod + time
T_ADD TOD / Time
tod + time
T_SUB TOD / Time
tod + dint
T_ADD TOD / Time
tod + dint
T_SUB TOD / Time
dt + time
T_ADD DT / Time
dt + time
T_SUB DT / Time
ldt – ldt
T_DIFF LDT
dtl – dtl
T_DIFF DTL
dt – dt
T_DIFF DT
date – date
T_DIFF DATE
ltod – ltod
T_DIFF LTOD
date + ltod
T_COMBINE DATE / LTOD
date + tod
T_COMBINE DATE / TOD
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4 Hardware-Independent Programming
4.1 Data types of S7-300/400 and S7-1200/1500
4
Hardware-Independent Programming
To make sure that a block can be used on all controllers without any further
adjustments, it is important not use hardware-dependent functions and properties.
4.1
Data types of S7-300/400 and S7-1200/1500
Below is a list of all elementary data types and data groups.
Recommendation
Only use the data types that are supported by the controllers on which the
program is to run.
Table 4-1: Elementary data types correspond to standard EN 61131-3
Description
S7-1200
S7-1500
S7-1200
S7-1500
BOOL
BYTE
WORD
DWORD
LWORD
Character type
CHAR (8 bit)
Numerical data
types
INT (16 bit)
DINT (32 bit)
REAL (32 bit)
SINT (8 bit)
USINT (8 bit)
UINT (16 bit)
UDINT (32 bit)
LREAL (64 bit)
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Bit data types
S7 300/400
LINT (64 bit)
ULINT (64 bit)
Time types
TIME
DATE
TIME_OF_DAY
S5TIME
LTIME
L_TIME_OF_DAY
Table 4-2: Data groups that are made up of other data types
Description
Time types
S7 300/400
DT
(DATE_AND_TIME)
DTL
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4 Hardware-Independent Programming
4.2 No bit memory but global data blocks
Description
S7 300/400
S7-1200
S7-1500
LDT
(L_DATE_AND_TIME)
Character type
STRING
Field
ARRAY
Structure
STRUCT
1)
1)
For S7-1500 the ARRAY data type is limited to 64 bit instead of 16 bit
Table 4-3: Parameter types for formal parameters that are transferred between blocks
Description
Pointer
S7 300/400
S7-1200
S7-1500
POINTER
ANY
1)
VARIANT
Blocks
TIMER
COUNTER
2)
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BLOCK_FB
BLOCK_FC
BLOCK_DB
BLOCK_SDB
VOID
PLC data types
1)
PLC Data Type
For optimized accesses, only symbolic addressing is possible
2)
Copyright
For S7-1200/1500 the TIMER and COUNTER data type is represented by
IEC_TIMER and IEC_Counter.
4.2
No bit memory but global data blocks
Advantages
Optimized global DBs are clearly more powerful than the bit memory address
area that is not optimized for reasons of compatibility.
Recommendation
The handling with bit memory is problematic, since every controller has a bit
memory address area with a different size. Do not use bit memory for the
programming but always global data blocks. This is how the program can
always be used universally.
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4 Hardware-Independent Programming
4.3 Programming of "clock bits"
4.3
Programming of "clock bits"
Recommendation
For the programming of clock memory bits, the hardware configuration always has
to be correct.
Use a programmed block as clock generator. Below, you can find a programming
example for a clock generator in the SCL programming language.
Example
The programmed block has the following functions. A desired frequency is
specified. The “Q” output is a Boolean value that toggles in the desired frequency.
The “Countdown” output outputs the remaining time of the current state of “Q”.
If the desired frequency is smaller or equal 0.0, then the output Q = FALSE and
Countdown = 0.0.
FB
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Q [Bool]
0.5
Period: 2 seconds
Frequency [Real]
Countdown [Time]
Note
TRUE
T#0S_703MS
The complete programming example is available for free download in the
following entry:
http://support.automation.siemens.com/WW/view/en/87507915
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5 The Most Important Recommendations
5
The Most Important Recommendations
Use optimized blocks
–
Chapter 2.6 Optimized blocks
Structuring the program clearly and well
–
Chapter 3.2 Organization blocks (OB)
Inserting instructions as multi-instance (TON, TOF ..)
–
Chapter 3.2.5 Multi-instances
Reusable programming of blocks
–
Chapter 3.2.8 Reusability of blocks
Symbolic programming
–
Chapter 3.6 Symbolic addressing
When handling data, work with ARRAY
–
Chapter 3.6.2 ARRAY data type and indirect field accesses
Creating PLC data types
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–
Chapter 3.6.3 STRUCT data type and PLC data types
Using libraries for storing program elements
–
Chapter 3.7 Libraries
No memory bits but global data blocks
–
Chapter 4.2 No bit memory but global data blocks
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6 Related Literature
6
Related Literature
Table 6-1
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Topic
Title
\1\
Siemens Industry Online Support
http://support.automation.siemens.com
\2\
Download page of the entry
http://support.automation.siemens.com/WW
/view/en/81318674
\3\
TIA Portal - An Overview of the Most
Important Documents and Links
http://support.automation.siemens.com/WW
/view/en/65601780
\4\
STEP 7 (TIA Portal) manuals
http://support.automation.siemens.com/WW
/view/en/29156492/133300
\5\
S7-1200 Manuals
http://support.automation.siemens.com/WW
/view/en/34612486/133300
\6\
S7-1500 Manuals
http://support.automation.siemens.com/WW
/view/en/56926743/133300
\7\
S7-1200 Getting Started
http://support.automation.siemens.com/WW
/view/en/39644875
\8\
S7-1500 Getting Started
http://support.automation.siemens.com/WW
/view/en/78027451
\9\
SIMATIC S7-1200 / S7-1500
Comparison list for programming
languages
http://support.automation.siemens.com/WW
/view/en/86630375
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7 History
7
History
Table 7-1
Date
V1.0
09/2013
First version
V1.1
10/2013
Corrections in the following chapters:
2.6.3 Best possible data storage in the processor on S7-1500
2.12 Internal reference ID for controller and HMI tags
3.2.2 Functions (FC)
3.2.3 Function blocks (FB)
3.4.3 Local memory
V1.2
03/2014
New chapter:
2.6.4 Conversion between optimized and non-optimized tags
2.6.5 Communication with optimized data
2.9.2 MOVE instructions
2.9.3 RUNTIME
3.6.4 Access to I/O areas with PLC data types
Extension of following chapter:
2.2 Terms
2.3 Programming languages
2.6 Optimized blocks
2.8.2 Date_Time_Long data type
2.10 Symbolic and comments
3.2 Program blocks
3.5 Retentivity
4.3 Programming of "clock bits"
Several corrections in different chapter
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Version
Programming Guideline for S7-1200/1500
V1.2, Entry ID: 81318674
Modifications
74