Short summary for Siemens forum

I have a Modbus TCP client on a PLC trying to read registers from a CM1542‑1 module. The PLC is at 172.20.10.60 and the CM is at 172.20.10.55:702. Client parameters (IP, port, Unit ID, start address and quantity) were configured per documentation, and I tested both zero‑based and 3xxxx conventions (2000 / 32001). The CM port remains closed or the CM immediately closes the TCP connection. Module/PLC logs show messages 7001 and Modbus exception response 0x80 0xC5. This is a remote target, which adds challenges for hands‑on checks (limited physical access, remote firewall/NAT, and delayed log retrieval). I have tried multiple Unit IDs and offsets and verified basic LAN connectivity from my side.

Question

Can anyone confirm the exact meaning of error code 7001 and Modbus exception 0xC5 on the CM1542‑1, and advise which CM configuration parameters to verify first (interface binding, Modbus service enable, port binding, access control, firmware) given that the device is remote and network constraints may apply? Also, what quick remote diagnostics should I run (netstat, Wireshark SYN/SYN‑ACK/RST capture, CM logs or diagnostic counters) to identify why the CM port stays closed and how to safely proceed without physical access.