Modbus is a serial communications protocol originally published by Modicon (now Schneider Electric) in 1979 for use with its programmable logic controllers (PLCs). Modbus has become a de facto standard communication protocol and is now a commonly available means of connecting industrial electronic devices.
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. Modbus is often used to connect a supervisory computer with a remote terminal unit (RTU) in supervisory control and data acquisition (SCADA) systems. Many of the data types are named from industry usage of Ladder logic and 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 TCP/IP is a simple Modbus protocol running on Ethernet over a TCP interface. Modbus is an application protocol that assigns the ways of managing and passing data between various layers without being affected by the protocol used by the next immediate layer.
Modbus TCP/IP uses Transmission Control Protocol (TCP) and Internet Protocol (IP) for the transmission of messages from Modbus between compatible devices over various systems. That is, Modbus TCP/IP uses a physical network (Ethernet), with a networking standard (TCP/IP), and itself offers a method of representing data (Modbus as the application protocol). A Modbus TCP/IP message is basically just a Modbus communication data message compressed in an Ethernet TCP/IP cover. TCP/IP is simply a transport layer protocol and does not change the way data is stored or interpreted inside the message.
PRECISE-LOG series of WIFI data loggers is now part of the Modbus family. It can be easily configured as a Modbus Server/Slave device. A standard Modbus master or client can talk to these data loggers and collect real-time data from them over Ethernet WIFI connection. Fore detailed instructions please refer to How to enable Modbus protocol to a PRECISE-LOG data logger