Advanced PLC Operations

The client API includes PLC management operations in addition to memory reads and writes. Availability depends on the PLC family, firmware, protection level, and current CPU state. A PLC can reject a valid request that it does not implement.

The examples below use Client. The corresponding AsyncClient methods have the same purpose and must be awaited.

Identification and diagnostics

Read common identification and status records after connecting:

order_code = client.get_order_code()
cpu_info = client.get_cpu_info()
cp_info = client.get_cp_info()
protection = client.get_protection()
state = client.get_cpu_state()
diagnostics = client.read_diagnostic_buffer()

For records without a convenience method, use read_szl(szl_id, index) or read_szl_list(). SZL layouts vary between PLC generations; the typed helpers in snap7.szl parse the layouts used by the convenience methods.

CPU state and clock

plc_stop(), plc_hot_start(), and plc_cold_start() change CPU state. Clock operations are provided by get_plc_datetime(), set_plc_datetime(), and set_plc_system_datetime().

Warning

CPU control and clock changes affect a real controller. Confirm that the operation is safe for the machine and process before issuing it.

Block operations

Use list_blocks() and list_blocks_of_type() to enumerate blocks, get_block_info() to inspect one, upload() or full_upload() to read one, and download() or delete() to modify the PLC. compress() and copy_ram_to_rom() expose the corresponding PLC maintenance operations.

These methods transfer individual PLC blocks; they do not create a complete TIA Portal project or full PLC backup.

Session passwords

For classic S7 CPUs configured with a session password, authenticate after connecting and clear the password before disconnecting:

client.connect("192.168.1.10", 0, 2)
client.set_session_password("secret")
try:
    data = client.db_read(1, 0, 4)
finally:
    client.clear_session_password()
    client.disconnect()

Forcing inputs and outputs

force_bit() and cancel_force() support the Area.PE input and Area.PA output areas. read_force_table() returns active force entries when the PLC supports SZL 0x0025:

from s7.type import Area

client.force_bit(Area.PA, byte_offset=0, bit=1, value=True)
active_forces = client.read_force_table()
client.cancel_force(Area.PA, byte_offset=0, bit=1)

Warning

A force overrides normal process behavior and can remain active after the application exits. Track every applied force and cancel it deliberately.

Raw protocol and compatibility operations

iso_exchange_buffer() sends a caller-provided S7 PDU. The as_* methods and completion callbacks preserve compatibility with the historical Snap7 API; new asynchronous applications should normally use AsyncClient instead. See Client for the complete method reference.