Server Setup for Testing

The built-in server lets you test your client code without a physical PLC.

Basic Server Example

from s7.server import Server
from s7.type import SrvArea
from ctypes import c_char

# Create and configure the server
server = Server()

# Register a data block (DB1) with 100 bytes
db_size = 100
db_data = bytearray(db_size)
db_array = (c_char * db_size).from_buffer(db_data)
server.register_area(SrvArea.DB, 1, db_array)

# Start the server on a non-privileged port
server.start(tcp_port=1102)

Client-Server Round Trip

from s7 import Client
from s7.server import Server
from s7.type import SrvArea
from ctypes import c_char

# --- Server setup ---
server = Server()
db_size = 100
db_data = bytearray(db_size)
db_array = (c_char * db_size).from_buffer(db_data)
server.register_area(SrvArea.DB, 1, db_array)
server.start(tcp_port=1102)

# --- Client connection ---
client = Client()
client.connect("127.0.0.1", 0, 1, tcp_port=1102)

# Write data
client.db_write(1, 0, bytearray([0x01, 0x02, 0x03, 0x04]))

# Read it back
data = client.db_read(1, 0, 4)
print(f"Read back: {list(data)}")  # [1, 2, 3, 4]

# Clean up
client.disconnect()
server.stop()

Registering Multiple Areas

from s7.server import Server
from s7.type import SrvArea
from ctypes import c_char

server = Server()

# Register DB1
db1_data = bytearray(100)
db1 = (c_char * 100).from_buffer(db1_data)
server.register_area(SrvArea.DB, 1, db1)

# Register DB2
db2_data = bytearray(200)
db2 = (c_char * 200).from_buffer(db2_data)
server.register_area(SrvArea.DB, 2, db2)

# Register merker area (256 bytes)
mk_data = bytearray(256)
mk = (c_char * 256).from_buffer(mk_data)
server.register_area(SrvArea.MK, 0, mk)

server.start(tcp_port=1102)

Note

Use a port number above 1024 (e.g., 1102) to avoid requiring root/admin privileges. Port 102 is the standard S7 port but is in the privileged range.

Using the Mainloop Helper

For quick testing, the mainloop function from the s7 package starts a server with common data blocks pre-registered:

from s7.server import mainloop

# Blocks the current thread
mainloop(tcp_port=1102)