Modbus ASCII - This is used in serial communication & makes use of ASCII characters for protocol communication.Modbus messages are framed (separated) by idle (silent) periods. A Modbus RTU message must be transmitted continuously without inter-character hesitations.
Modbus RTU is the most common implementation available for Modbus. The RTU format follows the commands/data with a cyclic redundancy check checksum as an error check mechanism to ensure the reliability of data. Modbus RTU - This is used in serial communication & makes use of a compact, binary representation of the data for protocol communication.There are many variants of Modbus protocols: Versions of the Modbus protocol exist for serial port and for Ethernet and other protocols that support the Internet protocol suite. The Modbus Organization is an association of users and suppliers of Modbus compliant devices that seeks to drive the adoption and evolution of Modbus.
The development and update of Modbus protocols has been managed by the Modbus Organization since April 2004, when Schneider Electric transferred rights to that organization. Many of the data types are named from its use in driving relays: a single-bit physical output is called a coil, and a single-bit physical input is called a discrete input or a contact. Modbus is often used to connect a supervisory computer with a remote terminal unit (RTU) in supervisory control and data acquisition (SCADA) systems. Modbus enables communication among many devices connected to the same network, for example a system that measures temperature and humidity and communicates the results to a computer.