MODBUS Application Protocol SPecification V1.1b3

Introduction

MODBUS is an application layer messaging protocol for client/server communication between devices connected on different types of buses or networks.

It is currently implemented using:

• TCP/IP over Ethernet. See MODBUS Messaging Implementation Guide V1.0a.
• Asynchronous serial transmission over a variety of media (wire : EIA/TIA -232-E, EIA-422, EIA/TIA-485-A; fiber, radio, etc.)
• MODBUS PLUS, a high speed token passing network.