Various Flavors of Modbus
Modbus protocol comes in several versions tailored for both serial ports and Ethernet connections. The most common variants include:
Modbus ASCII Protocol
Modbus ASCII protocol builds upon Modbus RTU by encoding instructions into ASCII characters for transmission. For instance, while Modbus RTU needs just one byte to transmit “12,” Modbus ASCII protocol requires converting “1” to “31” and “2” to “32,” thus using two bytes. Consequently, Modbus ASCII is less efficient and exhibits lower utilization rates.
Modbus Plus Protocol
Modbus Plus protocol, also known as MB+, is a high-speed Fieldbus network. It serves as a typical token bus network and a local area network system, primarily designed for industrial control applications.
Modbus TCP Protocol
Modbus TCP protocol is employed for managing and controlling automation equipment. It extends the usage of Modbus messages to “Intranet” and “Internet” environments through the TCP/IP protocol. Think of it as Modbus RTU protocol running on Ethernet.
Modbus RTU Protocol
The Modbus protocol is a necessity for communication between devices, specifically requiring Modbus RTU protocol. This stipulation is part of the Modbus protocol’s default mode. The frame structure typically comprises an address, function code, data, and a check.