ABB RVT Serie Instrucciones De Instalación Y De Funcionamiento página 494

The complete Modbus TCP/IP Application Data Unit is embedded into the data field of
a standard TCP frame and sent via TCP to well-known system port 502, which is
specifically reserved for Modbus applications. Modbus TCP/IP clients and servers listen
and receive Modbus data via port 502.
Modbus TCP must establish a connection before transferring data, since it is a
connection-based protocol. The Master (or Client in Modbus TCP) establishes a
connection with the Slave (or Server). The Server waits for an incoming connection from
the Client. Once a connection is established, the Server then responds to the queries
from the Client until the client closes the connection.
The number of Clients connected to 1 specific RVT is limited to 5.
In summary:
- Modbus TCP allows the user to connect to a RVT12-3P through Ethernet or
Internet using Modbus standard protocol (with HMI, SCADA...)
- The slave address of Modbus RTU specification is replaced by the IP address via
TCP port 502.
- Multiple Clients may access multiple RVT Servers.
12 Modbus protocol overview ç RVT communication