MODBUS is an application layer messaging protocol, positioned at level 7 of the OSI model,that provides client/server communication between devices connected on different types of buses or networks. The industry’s serial de facto standard since 1979, MODBUS continues to enable millions ofautomation devices to communicate. Today, support for the simple and elegant structure of MODBUS continues to grow. The Internet community can access MODBUS at a reserved system port 502 on the TCP/IP stack. MODBUS is a request/reply protocol and offers services specified by function codes. MODBUS function codes are elements of MODBUS request/reply PDUs The MODBUS protocol allows an easy communication within all types of network architectures.
Check here for more information about Modbus https://en.wikipedia.org/wiki/Modbus
This softwares is a Modbus TCP Client and was developed in Qt You can see the sofware working in this link: https://youtu.be/80lYV0ZqiZ4