User guide

In This Chapter
Chapter 11 Configuring the Digi Device for IA 57
Chapter 11 Configuring the Digi Device for IA
In This Chapter
This chapter describes how to configure Digi One/PortServer TS 2/4 MEI for use in an IA (industrial
automation) environment.
Configuring Modbus......................................................................................................................62
Configuring the User-Defined Protocol.........................................................................................63
Configuring Modbus
About the Modbus Serial-Port Protocols
Modbus is a protocol that defines how devices in an industrial automation (IA) environment
communicate. It specifies that a controlling unit, called a master, manages one or more units, called
slaves. The protocol specifies that only the master may initiate communication. Slaves may only respond.
The protocol defines the structure of Modbus messages, determines how the master requests information
from the slave or specifies an action for the slave to take, defines how the slave is to respond, specifies
addressing conventions, and deals with many of the other details required for communication to occur.
Modbus defines two encoding schemes, Modbus ASCII and Modbus RTU. Each Modbus device uses one
or the other.
Designed to function over a serial communication cable, Modbus has been extended in recent years to
function over an Ethernet network using Modbus/TCP, which defines a method of encapsulating Modbus
ASCII or Modbus RTU messages in IP packets for transport over the network.
The extermely flexible Digi implementation includes support for Modbus ASCII, Modbus RTU,
Modbus/TCP, and two other methods of transport over a network, TCP socket and UDP socket
communication. The implementation enables multiple network-based masters to concurrently initiate
communication with serial-based slaves using any of the supported network protocols.