Connecting to PLCs

This page shows how to connect to different Siemens PLC models using python-snap7.

Rack/Slot Reference 

PLC Model	Rack	Slot	Notes
S7-300	0	2
S7-400	0	3	May vary with multi-rack configurations
S7-1200	0	1	PUT/GET access must be enabled in TIA Portal
S7-1500	0	1	PUT/GET access must be enabled in TIA Portal
S7-200 (serial PPI)	–	–	Use `PPIClient` and a serial interface; see S7-200 Serial PPI.
LOGO! / S7-200 (Ethernet)	–	–	Use `Logo` or the controller’s documented TSAP values.

Warning

S7-1200 and S7-1500 PLCs ship with PUT/GET communication disabled by default. Enable PUT/GET in TIA Portal under the CPU properties before using s7.Client. See TIA Portal Configuration for step-by-step instructions.

S7-300 

from s7 import Client

client = Client()
client.connect("192.168.1.10", 0, 2)

S7-400 

from s7 import Client

client = Client()
client.connect("192.168.1.10", 0, 3)

S7-1200 / S7-1500 (PUT/GET)

If PUT/GET access is enabled in TIA Portal, you can also use the legacy protocol:

from s7 import Client

client = Client()
client.connect("192.168.1.10", 0, 1)

S7-200 Serial PPI 

Serial S7-200 connections use PPIClient, not rack/slot or TSAP addressing:

from s7 import PPIClient

with PPIClient("/dev/ttyUSB0", station=2, baudrate=9600) as client:
    data = client.v_read(0, 4)

Install python-snap7[ppi] and see S7-200 Serial PPI for supported areas and limitations.

LOGO! and Ethernet TSAP Connections 

For LOGO!, prefer the dedicated Logo class. Controllers that expose classic S7 over Ethernet with explicit TSAPs can use set_connection_params() before connecting:

from s7 import Client

client = Client()
client.set_connection_params("192.168.1.10", 0x1000, 0x2000)
client.connect("192.168.1.10", 0, 0)

The TSAP values are controller and project specific; the example values are not universal defaults.

Using a Non-Standard Port 

from s7 import Client

client = Client()
client.connect("192.168.1.10", 0, 1, tcp_port=1102)

Routing (Multi-Subnet Access)

Warning

Routing support is experimental and may change in future versions.

When the target PLC sits on a different subnet behind a gateway PLC, use connect_routed to let the gateway forward the connection:

from s7 import Client

client = Client()
client.connect_routed(
    host="192.168.1.1",       # gateway PLC address
    router_rack=0,            # gateway rack
    router_slot=2,            # gateway slot
    subnet=0x0001,            # target subnet ID
    dest_rack=0,              # target PLC rack
    dest_slot=3,              # target PLC slot
)
data = client.db_read(1, 0, 4)
client.disconnect()

Legacy `snap7` Package 

If you have existing code using snap7.Client, it continues to work unchanged — snap7 is an alias for s7:

import snap7

client = snap7.Client()
client.connect("192.168.1.10", 0, 1)

Asynchronous Connections 

AsyncClient provides native asyncio I/O and serializes request/response cycles on its connection:

import asyncio
from s7 import AsyncClient

async def main():
    async with AsyncClient() as client:
        await client.connect("192.168.1.10", 0, 1)
        data = await client.db_read(1, 0, 4)

asyncio.run(main())