Siemens S7 Devices Connector

S7 300/400/1200/1500

Overview

Channel Configuration

Protocol Options

The Siemens connector supports two optional XML properties that control how the driver resolves the data type for bit-addressable bytes. Both default to back-compatible behavior; setting them is opt-in.

RespectUserConfigDataType

Root element under the driver configuration. Controls whether the driver honors the user-configured Data Type on the Communication Point when the parsed address suffix would imply a different type.

• Default: false — driver overrides Data Type based on the parsed address suffix (back-compatible behavior).
• When set to true: driver keeps the Point's configured Data Type. Required for accurate bit extraction when reading a single bit from a byte whose other bits are also active.

AllowConfigDataType

Attribute on the <Address> element. Enables the per-address Data-Type override mechanism that RespectUserConfigDataType reads.

• Default: false.
• When set to true: the address parser propagates the user-configured Data Type to the runtime read path.

Activating user-controlled Data Type

All three of the following must be set together:

1. <Address AllowConfigDataType="true"> in the driver XML.
2. <RespectUserConfigDataType>true</RespectUserConfigDataType> in the driver XML.
3. The Communication Point's Data Type set to Byte.

When any one of the three conditions is absent, the driver retains its prior (back-compatible) behavior.

Node Configuration

Station Configuration

Station syntax: <IP  Address> ; <Rack>; <Slot>;<S7 Family>

• <IP Address>: IP address of the slave device in the Siemens network
•  <Rack>: Rack of the device
•  <Slot>: Slot of the device 
•  <S7 Family>: Model of the device. The options are:

300/400: Support for PLC Siemens S7-300 and S7-400 Series

1200: Support for PLC Siemens S7-1200 and S7-1500 Series

Points Configuration

Address

The syntax for the Siemens communication points is: <Type>:<Format><Address>.< Bit or String Length >

For DataBlock type: DB<DB Group>:<Format><Address>.<Bit or String Length>

Where:

• <Type>  is the register type. Valid values are: 
  • M=Flags
  • T=Timers
  • C=Counters
  • I=Inputs
  • Q=Outputs
  • DB=Data Blocks.
• <DB Group> is the group number of the configured Data Block type.
• <Address> is the device address.
• <Format>  is the format to treat the value from or to the device. Valid values are:
  • B=Byte
  • W=Word
  • DW=Dword
  • F=Float
  • ST=String
• <Bit or String Length> is the bit number. This parameter is optional. If you use the String type, it represents the String length.

The address is a single concatenated string with this structure: <Block><DBNumber><DataType><Address>.<BitOrStringLength>. Examples:

• MW0 — Flag (Merker) word at address 0
• IB0 — Input byte at address 0
• QB4 — Output byte at address 4
• DB1DW0 — Data Block 1, DWord at address 0
• DB5DBB10 — Data Block 5, Byte at address 10
• DB1DBST0.50 — Data Block 1, String at address 0, length 50
• DB1DBW0.3 — Data Block 1, Word at address 0, bit 3
• Block prefixes: M (Flag/Merker), T (Timer), C (Counter), I (Input), Q (Output), DB (Data Block)
• Data types: B (Byte→Char), W (Word→Short), DW (DWord→Integer), F (Float→Single), ST (String→ASCII), .DBB (DB Byte), .DBW (DB Word), .DBDW (DB DWord), .DBF (DB Float), .DBSTR/.DBST (DB String)

String Layout (DBSTR / DB String)

When an address uses the .DBSTR or .DBST suffix, the value on the PLC occupies N+2 bytes: a 2-byte header followed by N data bytes. The first header byte holds the declared maximum length, the second holds the current length, and the remaining N bytes hold the ASCII characters. This matches the Siemens S7 native STRING type. The driver handles the N+2 byte layout automatically — you address the string by its starting offset and declared length (for example DB1DBST0.50) and the runtime read/write path strips or builds the 2-byte header transparently. Reserve length + 2 bytes in the Data Block when sizing memory.

Error Code Reference

Driver Revision History

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