Siemens S7 Plus Devices Connector

S7 300/400/1200/1500

Overview

Channel Configuration

Protocol Options

The SiemensPlus connector exposes a Respect User Config Data Type option that controls how the driver resolves the data type for bit-addressable bytes.

RespectUserConfigDataType

A checkbox in the channel's Protocol Options. Controls whether the driver honors the user-configured Data Type on the Communication Point instead of overwriting it from the parsed address suffix.

• 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.

Example — reading a single bit with Data Type = Byte

A read-only tag pointing to bit 0 of a byte (e.g. DB1.DBB10.0) can misreport its value when another bit of the same byte is set. To read it correctly:

1. Enable Respect User Config Data Type in the channel's Protocol Options.
2. On the Communication Point, set Data Type to Byte.

With this configuration, when the PLC byte holds 0x80 (bit 7 ON, bit 0 OFF), the bit-0 tag correctly reads FALSE. Without it, the same tag would incorrectly read TRUE.

BlockSize

Defines the maximum amount of items per group, the default value is 512. Some devices support larger blocks, increase it to improve performance, or lower it if the PLC rejects the request.

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>.<DB Format><Address>.<Bit or String Length>

There is no separator between the register type and the format. The only separators are the dot after the DB Group number and the dot before the optional 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. The valid tokens depend on the register type — Data Blocks require the DB-prefixed tokens, every other area requires the plain tokens. Do not mix the two sets:
  • For M, T, C, I and Q: B=Byte, W=Word, DW=Dword, F=Float, ST=String, C=Counter, T=Timer
  • For DB: DBB=Byte, DBW=Word, DBDW=Dword, DBF=Float, DBSTR=String, DBST=Short 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>. The <DBNumber> and the dot that follows it appear only for DB addresses. Examples:

• MB0 — Flag (Merker) byte at address 0
• MW0 — Flag (Merker) word at address 0
• IB0 — Input byte at address 0
• QB4 — Output byte at address 4
• DB1.DBW0 — Data Block 1, Word at address 0
• DB1.DBDW0 — Data Block 1, DWord at address 0
• DB5.DBB10 — Data Block 5, Byte at address 10
• DB1.DBF8 — Data Block 1, Float at address 8
• DB1.DBB0.3 — Data Block 1, Byte at address 0, bit 3
• DB1.DBSTR0.52 — Data Block 1, String at address 0, STRING[50] (52 total bytes, see below)
• 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), C (Counter→Short), T (Timer→Short) for non-DB areas; DBB (DB Byte), DBW (DB Word), DBDW (DB DWord), DBF (DB Float), DBSTR / DBST (DB String) for DB areas, always written immediately after the dot that follows the DB number

A DB address written without that dot (DB1DW0), or with a colon in place of it (DB1:DW0), is not the accepted form. A plain token used inside a DB area (DB3.ST12.50) is invalid as well — use DB3.DBSTR12.50.

String Layout (DBSTR / DB String)

When an address uses the DBSTR or DBST format token, 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 length you write after the final dot is the total byte count, so for a STRING[N] you configure N + 2. For example, DB1.DBSTR0.52 addresses a STRING[50] starting at byte offset 0, and DB1.DBSTR16.26 addresses a STRING[24] starting at byte offset 16. Reserve those N + 2 bytes in the Data Block when sizing memory.

Adjacent tags: the next address starts after the N+2 bytes

Those N + 2 bytes are the field’s real footprint inside the Data Block, so the next tag must be configured at the first byte after them. DB21.DBSTR0.26 occupies bytes 0 through 25, which makes byte 26 the first free offset in DB21 — DB21.DBW26:

If the following tag is configured at an offset that falls inside the string range — DB21.DBW24, for example — every write to the string also lands on that tag’s address and replaces its value. Nothing writes to the numeric tag itself: the string write is what changes it.

Error Code Reference

Driver Revision History

In this section...