The Modbus protocol was originally developed and published by Modicon at the
beginning of the 80ies. The standard is primarily used in process automation.
Because of its openness and simplicity, it has become a de-facto industry
standard. The Modbus Organization
has taken care of its further development and updates, it also provides
all protocol-related documentation.
Modbus supports two different transmission modes:
supports communication via serial interfaces such as RS232, RS485
supports communication based on TCP/IP technologies
Modbus serial supports two different transmission modes:
uses binary data encoding
uses ASCII code for encoding data in readable character strings
Today, only Modbus RTU communication is still in practical use.
Modbus applies the master/slave principle, where one master can
communicate with one or several slaves. A slave can only respond to explicit
requests (polls) by the master.
Modbus supports only binary and 16-bit values, which are read in blocks by
the master, neither quality identifiers nor time stamps can be used.