User`s manual

Watlow EZ-ZONE™ Communications • 3 • Chapter 1

Chapter 1 PM Communications

EZ-ZONE™ PM & Communications

With the introduction of the first Programmable Logic Controllers (PLCs) in the early to mid 1970s it

quickly became apparent that there was a need to communicate between one PLC and another, and then on

a wider scale, between PLCs and other computers within the company infrastructure. Some of those needs

involved applications with interlinking processes, such as batch processes or assembly lines utilizing multiple

controls that required better synchronization and control.

Over time the scope of the requirements for industrial communications broadened and became better de-

fined, with specific needs being addressed. Those requirements and specifications centered on collecting data,

configuring controls, and controlling a process.

Protocols

Protocol describes how to exchange data. It also prevents two machines from attempting to send data at

the same time. There are a number of different data communications protocols in use today. The protocol part

of Watlow communications is very important, because it gives us a quality of communication that others often

don’t have. The EZ-ZONE™ PM family of controls provides several different protocols (Modbus RTU & TCP,

EtherNet/IP, and DeviceNet) meeting today's communication needs across many industrial applications.

In information technology, a protocol is the special set of rules that end points in a telecommunication

connection use when they communicate. Protocols exist at several levels in a telecommunication connection.

For example, there are protocols for the data interchange at the hardware device level and protocols for data

interchange at the application program level. In the standard model known as Open Systems Interconnec-

tion (OSI), there are one or more protocols at each layer in the telecommunication exchange that both ends

of the exchange must recognize and observe. Virtually all networks in use today are based in some fashion on

the OSI standard. OSI was developed in 1984 by the International Organization for Standardization (ISO),

a global federation of national standards organizations representing approximately 130 countries. As can be

seen below the OSI model is a set of seven layers that define the different stages that data must go through

to travel from one device to another over a network.

Figure 1.1