It is recommended to use the python-snap7 library, which provides comprehensive support for reading and writing the I/Q areas and DB blocks of Siemens S7 series PLCs. Below are two of the most commonly used examples:Reading and Writing I/Q Areas and Reading and Writing DB Blocks.1. Install
pip install python-snap7
2. Connect to the PLC
import snap7
# Create client
plc = snap7.client.Client()
# Connect to PLC (IP, rack, slot)
plc.connect(“192.168.0.1”, 0, 1)
print(“PLC Connected:”, plc.get_connected())
3. Read and Write I/Q Areas (Input/Output Image Area)
I Area = Inputs, Q Area = Outputs.
from snap7.util import get_bool, set_bool
# Read Q Area (Output Area), for example Q0.0
data = plc.read_area(snap7.types.Areas.PA, 0, 0, 1) # PA=Process Outputs
q0_0 = get_bool(data, 0, 0) # byte=0, bit=0
print(“Q0.0 =”, q0_0)
# Write Q0.0 = True
set_bool(data, 0, 0, True)
plc.write_area(snap7.types.Areas.PA, 0, 0, data)
4. Read and Write DB Blocks
Assuming there is an <span>INT</span> at offset 0 in DB1.
from snap7.util import get_int, set_int
# Read INT at offset 0 in DB1
data = plc.read_area(snap7.types.Areas.DB, 1, 0, 2) # DB1, offset 0, length 2 bytes
value = get_int(data, 0)
print(“DB1.DBB0 (INT) =”, value)
# Write new value 1234
set_int(data, 0, 1234)
plc.write_area(snap7.types.Areas.DB, 1, 0, data)
5. Explanation
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Areas.PE → Input Area (I)
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Areas.PA → Output Area (Q)
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Areas.DB → Data Block (DB)
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The offset and data type must match the definitions in the PLC program; otherwise, reading and writing errors will occur.
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<span>python-s7comm</span>library is more low-level, with strong protocol parsing capabilities, but in practical engineering, snap7 is more stable.
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