S7-Light (Step7)

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When trying to connect to a Siemens LOGO device, it is important to add one connection option, as Siemens seems to have only partially implemented the protocol, the device simply terminates the connection as soon as our driver tried to read the SZL table in order to find out which type of S7 device it is talking to. This can be disabled by passing in the type of PLC. For a Siemens LOGO device therefore please add ?controller-type=LOGO to the connection string.

The S7-Light driver is a stripped-down version of the full S7 driver. It’s main goal is to simplify communication for S7 devices, that do not support subscriptions, as under heavy load, these have proven to cause issues. As soon as we have rewritten the PLC4X SPI, we will most probably merge both back together again.

Connecting as easy as 1-2-3.

ONE

In PLC4X the URL philosophy is used as the data source for the connection for the specification of the driver and its connection parameters, this is almost a standard in network applications (pointing to the best practices). It is also possible to create an instance of the driver directly and assign its parameters with the typical "set" methods.

Note In the following, reference will be made to the Java-based driver, which implements all the functionalities indicated in this manual.

The specified URL has the structure

s7_url

  1. SCHEMA: Defines the protocol to be used, in our particular case S7

  2. DOMAINE NAME: Physical address of the PLC or CP’s.

  3. PARAMETERS: List of key/value values separated by ampersand "&". They define the behavior of the driver.

The SCHEMA and DOMAINE NAME are almost standard for any URL and do not require further explanation. The PARAMETERS that define the behavior of the driver are defined in the following table.

Connection String Options

Unresolved include directive in modules/users/pages/protocols/s7-light.adoc - include::partial$s7-light.adoc[]

Name Value Description

Supported Operations

read

Only supported with tcp transport.

write

Only supported with tcp transport.

TWO

After defining the URL, the connection is made. Driver selection from the URL is done via PLC4X’s SPI support, so driver instantiation and mapping originating from the URL is done transparently by the Java SPI services.

Any inconsistency in the URL definition will generate an exception that must be handled by the user program.

     .
     .
     .
try {
    PlcConnection connection  new DefaultPlcDriverManager().getConnection("s7://10.10.1.33?remote-rack=0&remote-slot=3&controller-type=S7_400"); //(2.1)
    final PlcReadRequest.Builder subscription  connection.readRequestBuilder(); //(2.2)
     .
     .
     .
     }

In (2.1) the driver instance is created, you only have to ensure that the required driver is in the CLASSPATH of your Java environment. Already in (2.2) it defines the type of service required (read/write or a subscription), here a read request is indicated.

No problems? Then we are ready to configure and request the data that we require from the PLC. Let’s go to step "three".

THREE

By having the connection we can start building and executing our requests.

.
.
.
 readrequest.addTagAddress("MySZL", "SZL_ID=16#0091;INDEX=16#0000"); //(3.1)

            final PlcReadRequest rr  readrequest.build(); //(3.2)
            final PlcReadResponse szlresponse  rr.execute().get(); //(3.3)
  if (szlresponse.getResponseCode("MySZL") = PlcResponseCode.OK) {//(3.4)
  }
.
.
.

In (3.1) the request for a PLCTag is constructed, in this particular case a list of controller system status. In step (3.2) we build the request and in (3.3) we execute the request using the futures pattern in Java. We verify in (3.4) that everything is fine and that our data was acquired.

These steps are shown separately for ease of analysis, but can be simplified into one statement to avoid excessive code.

A detailed explanation of the format for addressing PLCTags in the S7 driver will be given in the following sections.

Individual Resource Address Format

When programming Siemens PLCs, usually the tool used to do that is called TIA Portal.

The PLC4X S7 Driver is therefore sticking to the address format defined by this tool as it simplifies exchanging address information.

General Format

In general all S7 addresses have this format:

. %{Memory-Area}{start-address}:{Data-Type}[{array-size}]

If the array-part is omitted, the size-default of 1 is assumed.

Generally there are two types of addresses:

. Bit-Addresses {Memory-Area-Code}{Start-Byte-Address}.{Bit-Offset}:BOOL[{Count}]
. Byte-Addresses {Memory-Area-Code}{Start-Byte-Address}:{Data-Type-Code}[{count}]

Bit addresses are only used if the datatype: BOOL is used.

The array notation of these can be omitted. In this case a Count of 1 is used per default.

Start-Byte-Address and Bit-Offset in above list both represent unsigned integer values.

In case of accessing data in the data block memory area, the syntax is quite a bit more complex:

. DB{Data-Block-Number}.DB{Short-Data-Type-Code}{Start-Byte-Address}.{Bit-Offset}:BOOL[{Count}]
. DB{Data-Block-Number}.DB{Short-Data-Type-Code}{Start-Byte-Address}:{Data-Type-Code}[{Count}]

When reading a STRING datatype, currently 254 characters would automatically be fetched from the PLC.

In order to limit the amount of data, we extended the STRING type declaration syntax to allow limiting this.

With the following format less than 254 characters can be read:

. DB{Data-Block-Number}.DB{Short-Data-Type-Code}{Start-Byte-Address}:STRING({string-length})[{Count}]

These addresses can usually be copied directly out of TIA portal. However we also implemented a shorter version, as above version does have some unnecesary boilerplate parts (The .DB in the middle as well as the Short-Data-Type-Code)

The shorter syntax looks like this:

. DB{Data-Block-Number}:{Start-Byte-Address}.{Bit-Offset}:BOOL[{Count}]
. DB{Data-Block-Number}:{Start-Byte-Address}:{Data-Type-Code}[{Count}]
. DB{Data-Block-Number}:{Start-Byte-Address}:STRING({string-length})[{Count}]

The S7 driver will handle both types of notation equally.

Memory Areas

The S7 driver currently allows access to the following memory areas.

The Code column represents the code that is used in above general address syntax:

Not all S7 device types support the same full set of memory areas, so the last column gives more information on which types a given memory area is supported on.

Code Name Description Supported PLC Types

C

COUNTERS

TODO: Document this

TODO: Document this

T

TIMERS

TODO: Document this

TODO: Document this

D

DIRECT_PERIPHERAL_ACCESS

TODO: Document this

TODO: Document this

I

INPUTS

Inputs (Digital and Analog …​ usually Analog Inputs just have a start-address offset to separate them from the digital ones)

All

Q

OUTPUTS

Outputs (Digital and Analog …​ usually Analog Outputs just have a start-address offset to separate them from the digital ones)

All

M

FLAGS_MARKERS

TODO: Document this

TODO: Document this

DB

DATA_BLOCKS

Memory areas containing user-defined data structures usually accessed by the integer data block number. antease note that data block addresses have a little more complex address format.

All

DBI

INSTANCE_DATA_BLOCKS

TODO: Document this

TODO: Document this

LD

LOCAL_DATA

TODO: Document this

TODO: Document this

Data Types

Code Short-Code Name Description Size in bits Supported PLC Types

Bit-Strings (Will all interpreted as sequence of boolean values in PLC4X)

BOOL

X

Bit

Single boolean value

1

All

BYTE

B

Byte

Array of 8 boolean values

1

All

WORD

W

Word

Array of 16 boolean values

2

All

DWORD

D

Double-Word

Array of 32 boolean values

4

All

LWORD

X

Long-Word

Array of 64 boolean values

8

S7_1500

Integer values

SINT

B

Small int

8 bit integer (signed)

1

S7_1200, S7_1500

USINT

B

Small unsigned int

8 bit integer (unsigned)

1

S7_1200, S7_1500

INT

W

Integer

16 bit integer (signed)

2

All

UINT

W

Unsigned integer

16 bit integer (unsigned)

2

S7_1200, S7_1500

DINT

D

Double integer

32 bit integer (signed)

4

All

UDINT

D

Unsigned Double Integer

32 bit integer (unsigned)

4

S7_1200, S7_1500

LINT

X

Long integer

64 bit integer (signed)

8

S7_1500

ULINT

X

Unsigned long integer

64 bit integer (unsigned)

8

S7_1500

Floating point values

REAL

D

Real

32 bit IEEE 754 full precision floating point value (signed)

4

All

LREAL

X

Long Real

64 bit IEEE 754 double precision floating point value (signed)

8

S7_1200, S7_1500

Character values

CHAR

B

Character

8 bit character

1

All

WCHAR

X

Double byte character

16 bit character value

2

S7_1200, S7_1500

STRING

X

String

String 2 + n bytes

1

All

WSTRING

X

Double byte String

String of 16 bit characters 2 + n bytes

1

S7_1200, S7_1500

Temporal values

S5TIME

X

S5 Time

S5 Time (like in duration)

2

S7_300, S7_400, S7_1500

TIME

X

Time

Time (like in duration) (Minutes, Seconds, Milliseconds)

4

All

LTIME

X

Long Time

Long Time (like in duration) (Minutes, Seconds, Milliseconds, Microseconds, Nanoseconds)

8

S7_1500

DATE

X

Date

Date

2

All

TIME_OF_DAY

X

Time of day

Time (like in 4:40PM)

4

All

DATE_AND_TIME

X

Date and Time

Date and time (like in 03.05.2020 4:40 PM)

8

S7_300, S7_400, S7_1500

Some useful tips

Especially when it comes to the input- and output addresses for analog channels, the start addresses are configurable and hereby don’t always start at the same address. In order to find out what addresses these ports have, please go to the device setting of your PLC in TIA Portal

devsettings

Especially pay attention to this part:

iosettings

In above image you can see that this device has 8 digital inputs (DI 8) and 2 analog inputs (AI 2_1) as well as 6 digital outputs (DQ 6).

The start addresses of the digital inputs and outputs start directly at 0.

The analog inputs however start at address 64.

Each digital input and output can be addresses by a single bit-address (start-address and offset) or can be read in a block by reading a full byte starting at the given start address without providing a bit offset.

Resources

  1. https://snap7.sourceforge.net/

  2. https://support.industry.siemens.com/cs/document/13649203/simatic-net-pc-software-s7-programming-interface?dti=0&dl=en&lc=es-ES

  3. https://support.industry.siemens.com/cs/document/109797648/simatic-comparison-list-for-s7-300-s7-400-s7-1200-s7-1500?dti=0&lc=en-WW

  4. https://support.industry.siemens.com/cs/mdm/109746537?c=98956468747&lc=es-DO

  5. https://support.industry.siemens.com/cs/document/15166942/writing-user-specific-information-to-the-diagnostic-buffer-of-a-cpu-(sfc-52)?dti=0&lc=en-ES

  6. https://support.industry.siemens.com/cs/document/24013249/how-do-you-display-alarm_s-or-alarm_d-messages-with-process-values-(so-called-associated-values)-on-a-wincc-flexible-operator-panel-?dti=0&lc=en-WW

  7. https://support.industry.siemens.com/cs/document/109481157/comunicaci%C3%B3n-entre-paneles-de-operador-simatic-hmi-y-convertidores-de-frecuencia-sinamics-g120-para-el-manejo-y-la-visualizaci%C3%B3n-de-avisos-de-fallo-y-de-advertencia-(enlace-directo-sin-controlador)?dti=0&lc=es-WW

  8. https://support.industry.siemens.com/cs/document/97550333/sinamics-g-s-hmi-direct-access?dti=0&lc=en-WW

  9. https://support.industry.siemens.com/cs/document/21402122/technology-cpus-technology-template-error-messages-?dti=0&lc=en-WW

  10. https://support.industry.siemens.com/cs/document/77467239/transforming-warning-and-error-messages-of-a-sinamics-drive-with-the-aid-of-the-xml-parser-and-integrating-them-into-a-step-7-hmi-project?dti=0&lc=en-WW

  11. https://support.industry.siemens.com/cs/document/24037531/%C2%BFqu%C3%A9-pasos-de-configuraci%C3%B3n-hay-que-realizar-en-el-simotion-scout-y-el-wincc-flexible-para-que-se-muestren-los-avisos-alarm_s-y-las-alarmas-tecnol%C3%B3gicas-dentro-del-wincc-flexible-runtime-?dti=0&lc=es-ES