Tecfluid MX4B - Manual (Page 5)

5
MODBUS
1 INTRODUCTION
Modbus is a communication protocol commonly used to connect industrial electronic
devices. It is based in a master-slave architecture.
Protocol Modbus RTU uses a compact binary representation of the data and ends its
frames with a cyclic redundancy check code.
2 MODBUS DATA MODEL
Modbus bases its data model in four tables with differentiated characteristics.
Discrete Inputs: Read only bits. This type of data can be read by a master device. They
are not implemented in Tecfluid Modbus protocol devices.
Coils: Read write bits. These data can be read or written by a master device. They are
not implemented in Tecfluid Modbus protocol devices.
Input Registers: 16 bits read only data. This type of data can be read by a master
device.
Holding Registers: 16 bits read write data. These data can be read or written by a
master device.
3 MODBUS FUNCTIONS
Modbus functions allow access to a device in order to read or modify the value of some
of its data. The Tecfluid devices support the following functions:
3.1 Function “Read Input Registers” 0x04h
Gets the value of the "Input Registers" of one or more consecutive addresses of the
selected device.
3.2 Function “Read Holding Registers” 0x03h
Gets the value of the "Holding Registers" of one or more consecutive addresses of the
selected device.
3.3 Function “Write Single Register” 0x06h
Writes the value of a "Holding register" to the address of the selected device.
3.4 Function “Write Multiple Registers” 0x10h
Writes the value of the "Holding Registers" to several consecutive addresses of the
selected device.
4 MODBUS IN MX4B CONVERTER
4.1 Data access
The data that can be accessed in a MX4B converter and their format are the following: