Siemens S7

This input is tailored for the S7 communication protocol, facilitating a direct connection with S7-300, S7-400, S7-1200, and S7-1500 series PLCs.

For more modern PLCs like the S7-1200 and S7-1500 the following two changes need to be done to use them:

1. "Optimized block access" must be disabled for the DBs we want to access

2. In the "Protection" section of the CPU Properties, enable the "Permit access with PUT/GET" checkbox

Configuration

input:
  s7comm:
    tcpDevice: '192.168.0.1' # IP address of the S7 PLC (optionally with port, e.g., '192.168.0.1:102')
    rack: 0                  # Rack number of the PLC. Defaults to 0
    slot: 1                  # Slot number of the PLC. Defaults to 1
    batchMaxSize: 480        # DEPRECATED: This field never worked correctly because batches were calculated before connecting to the PLC, so the actual negotiated PDU size was unknown. PDU size is now automatically negotiated during connection.
    timeout: 10              # Timeout in seconds for connections and requests. Default to 10
    disableCPUInfo: false    # Set this to true to not fetch CPU information from the PLC
    addresses:               # List of addresses to read from
      - "DB1.DW20"     # Accesses a double word at location 20 in data block 1
      - "DB1.S30.10"   # Accesses a 10-byte string at location 30 in data block 1

Configuration Parameters

• tcpDevice: IP address or hostname of the Siemens S7 PLC, optionally with port (e.g., 192.168.0.1:102). If no port is specified, the default S7 port 102 is used.

• rack: Identifies the physical location of the CPU within the PLC rack.

• slot: Identifies the specific CPU slot within the rack.

• timeout: Timeout duration in seconds for connection attempts and read requests.

• disableCPUInfo: Set this to true to not fetch CPU information from the PLC. Should be used when you get the error 'Failed to get CPU information'

• addresses: Specifies the list of addresses to read. Addresses are automatically batched to respect protocol limits and PDU size. The format for addresses is <area>.<type><address>[.extra], where:

  • area: Specifies the direct area access, e.g., "DB1" for data block one. Supported areas include inputs (PE), outputs (PA), Merkers (MK), DB (DB), counters (C), and timers (T).

  • type: Indicates the data type, such as bit (X), byte (B), word (W), double word (DW), integer (I), double integer (DI), real (R), date-time (DT), and string (S). Some types require an 'extra' parameter, e.g., the bit number for X or the maximum length for S.

Output

Similar to the OPC UA input, this outputs for each address a single message with the payload being the value that was read. To distinguish messages, you can use meta("s7_address") in a following benthos bloblang processor.

Batching Behavior

Addresses are automatically split into batches based on S7 protocol constraints:

• Max 20 items per request: The S7 protocol limits AGReadMulti to 20 addresses per request

• PDU size: The request and response must fit within the negotiated PDU size (typically 240-480 bytes depending on the PLC model)

When more than 20 addresses are configured or the combined data exceeds PDU limits, multiple sequential requests are made. This has implications:

• Timing: Addresses in different batches are read at slightly different times, resulting in different timestamps

• Performance: More batches means more round-trips to the PLC, increasing total read time