It is clear that the direct use of Slave Modbus mode does not have any protection against reading or writing to PLC memory.
I haven't tried to do something like password protection, but I think it's possible to run your own exchange Modbus commands using the Protocol FB when starting the PLC.
Here are the possible options:
- set the password that must be set (writed) by master (using an address that does not exist in the PLC and own "Simulated Modbus" protocol) and put the PLC in full access Slave mode via standard Modbus (and disable "Simulated Modbus" protocol until the next restart of the PLC or the programmed standard modbus write command action - reset the password);
- create your "Local simulated Modbus" with a set of available cells for writing or only reading via Protocol FB.
I was building "My Modbus" to read a record of User defined Modbus codes in the range 65-72 (Not implemented in PLC). Everything worked without problems, so I think it's easy to create something like this to give write and read access to only specified cells using standard modbus codes or User defined Modbus codes.
Is it CPU-for-Panel present?
Panel cannot operate independently. CPU-for-Panel must be plugged
into the back of a UniStream® HMI panel. The panel provides the CPU’s
power source. The CPU-for-Panel comprises:
1 IO/COM Bus connector for interfacing Uni-I/O™ & Uni-COM™ modules
2 Isolated RS485 and CANbus ports 3 Backup battery