MODBUS

Defined

From: http://www.modbus.org/specs.php

MODBUS is an application-layer messaging protocol, positioned at level 7 of the OSI model. It provides client/server communication between devices connected on different types of buses or networks.

The de facto industrial serial standard since 1979, MODBUS continues to enable millions of automation devices to communicate. Today, support for the simple and elegant structure of MODBUS continues to grow. The Internet community can access MODBUS at a reserved system port 502 on the TCP/IP stack.

MODBUS is a request/reply protocol and offers services specified by function codes. MODBUS function codes are elements of MODBUS request/reply PDUs.

Simplified Explanation

• The MODBUS protocol was developed by MODICON in order to enable a standard way to communicate with distributed devices around a machine that are used for controlling the machine.
  
  

• The MODBUS protocol includes the ability to send a command with parameters to these various devices.
  
  

• The devices can be MOTION CONTROLLER modules, INPUT modules, OUTPUT modules, ANALOG modules, and any other module that can be used to control or sense the machinery.
  
  
  

So this is how data is transferred using this protocol:

------------ TCP/IP [ MODBUS DATA ] ---------------->
<----------- TCP/IP [ MODBUS DATA ] --------------

CNC Bender Uses MODBUS TCP/IP Enabled Modules

CNC Bender communicates with modules around the bender using this standard. Each module has a unique IP address. So the MODBUS data is sent to a module enclosed in a TCP/IP command.

Other References

For of list of MODBUS errors, see MODBUS Exception Responses