S7-Light (Step7)

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.

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

SCHEMA: Defines the protocol to be used, in our particular case S7
DOMAINE NAME: Physical address of the PLC or CP’s.
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

Name

Type

Default Value

Required

Description

Name

Siemens S7 (Basic) (light)

Code

s7-light

Maven Dependency

<dependency>
  <groupId>org.apache.plc4x</groupId>
  <artifactId>plc4j-driver-s7</artifactId>
  <version>pre-release</version>
</dependency>

Default Transport

tcp

Supported Transports

tcp

Config options:

local-rack

INT

Rack value for the client (PLC4X device).

local-slot

INT

Slot value for the client (PLC4X device).

local-device-group

STRING

OTHERS

Local Device Group. (Defaults to 'OTHERS').
Allowed values:
- PG_OR_PC
- OS
- OTHERS
Since: 0.13.0

local-tsap

INT

Local Transport Service Access Point. (Overrides settings made in local-rack, local-slot and local-device-group. Be sure to convert into integer representation)

remote-rack

INT

Rack value for the remote main CPU (PLC).

remote-slot

INT

Slot value for the remote main CPU (PLC).

remote-device-group

STRING

PG_OR_PC

Remote Device Group (Defaults to 'PG_OR_PC').
Allowed values:
- PG_OR_PC
- OS
- OTHERS

remote-tsap

INT

Remote Transport Service Access Point. (Overrides settings made in remote-rack, remote-slot and remote-device-group. Be sure to convert into integer representation)

pdu-size

INT

1024

Maximum size of a data-packet sent to and received from the remote PLC. During the connection process both parties will negotiate a maximum size both parties can work with and is equal or smaller than the given value is used. The driver will automatically split up large requests to not exceed this value in a request or expected response.

max-amq-caller

INT

Maximum number of unconfirmed requests the PLC will accept in parallel before discarding with errors. This parameter also will be negotiated during the connection process and the maximum both parties can work with and is equal or smaller than the given value is used. The driver will automatically take care not exceeding this value while processing requests. Too many requests can cause a growing queue.

max-amq-callee

INT

Maximum number of unconfirmed responses or requests PLC4X will accept in parallel before discarding with errors. This option is available for completeness and is correctly handled out during the connection process, however it is currently not enforced on PLC4X’s side. So if a PLC would send more messages than agreed upon, these would still be processed.

controller-type

STRING

As part of the connection process, usually the PLC4X S7 driver would try to identify the remote device. However some devices seem to have problems with this and hang up or cause other problems. In such a case, providing the controller-type will skip the identification process and hereby avoid this type of problem. Possible values are:/n- S7_300
- S7_400
- S7_1200
- S7-1500
- LOGO

read-timeout

INT

1000

This is the maximum waiting time for reading on the TCP channel. As there is no traffic, it must be assumed that the connection with the interlocutor was lost and it must be restarted. When the channel is closed, the "fail over" is carried out in case of having the secondary channel, or it is expected that it will be restored automatically, which is done every 4 seconds.

enable-block-read-optimizer

BOOLEAN

true

Enable the new experimental block-read optimizer, that groups tags in close memory proximity together and reads blocks of data instead of individual tags. This allows more data to be transferred in one request and is generally intended for cases in which a big number of tags are read.

Transport config options:

tcp

tcp.keep-alive

BOOLEAN

false

Should keep-alive packets be sent?

tcp.no-delay

BOOLEAN

true

Should packets be sent instantly or should we give the OS some time to aggregate data.

tcp.default-timeout

INT

1000

Timeout after which a connection will be treated as disconnected.

Name Value Description

Name	Value	Description
Supported Operations
	`read`	Only supported with `tcp` transport.
	`write`	Only supported with `tcp` transport.

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

Code

Name

Description

Supported PLC Types

COUNTERS

TODO: Document this

TIMERS

TODO: Document this

DIRECT_PERIPHERAL_ACCESS

TODO: Document this

INPUTS

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

All

OUTPUTS

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

All

FLAGS_MARKERS

TODO: Document this

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

LOCAL_DATA

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

Code

Short-Code

Name

Description

Size in bits

Supported PLC Types

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

BOOL

Bit

Single boolean value

All

BYTE

Byte

Array of 8 boolean values

All

WORD

Word

Array of 16 boolean values

All

DWORD

Double-Word

Array of 32 boolean values

All

LWORD

Long-Word

Array of 64 boolean values

S7_1500

Integer values

SINT

Small int

8 bit integer (signed)

S7_1200, S7_1500

USINT

Small unsigned int

8 bit integer (unsigned)

S7_1200, S7_1500

INT

Integer

16 bit integer (signed)

All

UINT

Unsigned integer

16 bit integer (unsigned)

S7_1200, S7_1500

DINT

Double integer

32 bit integer (signed)

All

UDINT

Unsigned Double Integer

32 bit integer (unsigned)

S7_1200, S7_1500

LINT

Long integer

64 bit integer (signed)

S7_1500

ULINT

Unsigned long integer

64 bit integer (unsigned)

S7_1500

Floating point values

REAL

Real

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

All

LREAL

Long Real

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

S7_1200, S7_1500

Character values

CHAR

Character

8 bit character

All

WCHAR

Double byte character

16 bit character value

S7_1200, S7_1500

STRING

String

String 2 + n bytes

All

WSTRING

Double byte String

String of 16 bit characters 2 + n bytes

S7_1200, S7_1500

Temporal values

S5TIME

S5 Time

S5 Time (like in duration)

S7_300, S7_400, S7_1500

TIME

Time

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

All

LTIME

Long Time

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

S7_1500

DATE

Date

All

TIME_OF_DAY

Time of day

Time (like in 4:40PM)

All

DATE_AND_TIME

Date and Time

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

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

Especially pay attention to this part:

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.

S7-Light (Step7)

Connecting as easy as 1-2-3.

ONE

Connection String Options

tcp

TWO

THREE

Individual Resource Address Format

General Format

Memory Areas

Data Types

Some useful tips

Resources