Understanding legacy network technologies

There are a few other communication technologies that you may also encounter in a Rockwell Automation solution. Some are legacy networks, while others are solution-specific technologies:

• Data Highway Plus(DH+)
• Universal Remote I/O (RIO)
• Serial Real-time Communications System (SERCOS)
• SynchLink
• DF1
• DH-485

In the following sections, we will introduce each of the legacy network technologies listed here.

Data Highway Plus

DH+ was used by older controllers (such as PLC-2, PLC-3, PLC-5, and SLC 500) for networking. It was developed as a proprietary protocol in the late '70s by Allen-Bradley. There are Logix communication modules available that can connect to the DH+ networks and can save customers from having to rip out and replace their older DH+ networks. DH+ supported remote programming and messaging over the network.

Specifically, it enabled uploading and downloading programs, forcing values, monitoring, and online edits. It is common to encounter DH+ networks still used in the field today, but it is obsolete, so we will not cover it in detail in this book.

In the following section, we will cover another legacy Rockwell network technology, called RIO.

RIO

RIO was also used by older controllers (such as PLC-2, PLC-3, PLC-5, and SLC 500) to communicate with the remote I/O chassis. There are Logix communication modules available that can connect to RIO and save the cost of replacing the RIO networks. Using a remote rack allows you to place the I/O modules closer to the actual devices with which they are communicating. The RIO rack connected back to the main controller using a two-wire Belden 9463 cable, also known as a blue hose cable. Although it is common to encounter RIO networks in the field today, it is also obsolete, so we will not cover it in detail here.

In the next section, we will introduce another serial communication protocol, called SERCOS.

SERCOS

SERCOS, or IEC 61491, is a communication technology created for real-time motion control. It provides high-speed serial communication over an electrical noise-immune fiber-optic cable and is commonly used in the manufacturing industry. It was developed by an international consortium of companies called Interest Group SERCOS, which included Siemens, ABB, AEG, AMK, Robert Bosch, and Indramat. Logix communication modules that can communicate with SERCOS devices for motion controlare available. However, we will not touch on motion control in this book, so we will not explore this communication technology in detail.

In the following subsection, we will briefly cover the SynchLink fiber-optic communication technology.

SynchLink

SynchLink is a fiber-optic communication technology for interfacing with PowerFlex 700 products. It is a streamlined protocol focused on high-speed drive and motion control. It does not transmit diagnostic information and should be used in conjunction with a standard control network, such as ControlNet or EtherNet/IP.

Next, we will cover the DH-485 and DF1 protocols in the following subsection.

DH-485 and DF1

The DH-485 and DF1 networks are legacy serial technologies that provided communication for the PLC-5, SLC 500, and MicroLogix controllers, as well as Human Machine Interface (HMI) terminals and computers. There are third-party communication modules available from ProSoft that allow DH-485 and DF1 to communicate with Logix devices. Although it is common to encounter DH-485 and DF1 in the field today, they have both been retired and so will not be covered in this book.

Now that we have introduced a myriad of Rockwell Network communication technologies, we will compare their capabilities in the next section.