Searching for a "Modbus Slave registration key" typically refers to the licensing credentials for a popular industrial simulation software called Modbus Slave , developed by Witte Software
explains how to use data loggers as Modbus servers (slaves) in SCADA networks. Application Note provides steps for configuring Mint-based ASCII slaves. Modbus Tools Warning on "Free" Keys modbus slave registration key
If you are a software developer building your own Modbus slave application and you want to implement a licensing system, here is a basic algorithm (do not copy this for commercial releases – it is insecure): Searching for a "Modbus Slave registration key" typically
Different software developers use different methods for registration and licensing. ModbusPoll (Modbus Slave) modbus slave registration key