What is the 1756-DHRIO and How Does it Work

If you want to send messages over a data highway plus network, you need special interface modules. These interface modules interact with the ControlLogix buses and initiate and control remote I/O communication and monitoring. We will talk about such a module today.

Such an interface module is the 1756-DHRIO. It is a ControlLogix Data Highway Plus remote i/o communication interface module. It provides a superior quality of functionality over previous similar creations. We will describe the functions of it below.

A 1756-DHRIO is one of the best network interface modules in the market. It can scan the remote i/o networks, by transferring discrete data as well as block transfer data with remote i/o devices. It can communicate between devices that are on a data highway plus network. It can also interact and send and receive messages on other other networks like ethernet or controlnet. This all is based upon the interface protocols, of course.

The Allen Bradley 1756-DHRIO data highway plus RIO module supports the following types of communications between devices on the same network: Data Highway Plus (DH+) messaging, Control and Information Protocol (CIP) messaging, and Remote I/O.

You can send messages between devices on DH+ networks and devices on other networks such as ControlNet, Ethernet, or other DH+ networks. A 1756-DHRIO channel functions as a scanner by using remote I/O functionality. The module transfers discrete and block-transfer data with remote I/O devices. This module enables connection to multiple remote I/O adapters.

What is Data Highway Plus?

On the most basic level, Data Highway Plus is a wire or cable and a protocol that connects computers and peripheral devices so that they can communicate. The wire used for a network is called the network medium.

A DH+ link transfers data between ControlLogix controllers, PLC and SLC controllers, and other devices that use the DH+ network. These devices are called stations. You can connect a maximum of 32 stations to one DH+ link.

Using 1756-DHRIO for Remote I/O

The remote I/O system lets you control I/O devices that are not in the controller’s chassis. A 1756-DHRIO channel, configured as a remote I/O scanner, transfers discrete and block-transfer data between a ControlLogix controller and remote I/O devices.

Follow these steps when setting up a remote I/O system:

  1. Configure the remote I/O adapter
  2. Layout the remote I/O network cable
  3. Connect the remote I/O network cable
  4. Configure the scanner channel

You can connect the following devices for doing remote i/o with this interface module:

  • enhanced PLC-5 processors 1785-LxxB
  • Ethernet PLC-5 processors 1785-LxxE
  • ControlNet PLC-5 processor 1785-LxxC
  • VMEbus PLC-5 processors 1785-VxxB
  • extended-local PLC-5 processors 1785-LxxL
  • classic PLC-5 processors 1785-LTx
  • SLC 500 Remote I/O Adapter Module 1747-ASB
  • 1791 Block I/O 1791 series
  • Remote I/O Adapter Module 1771-ASB
  • 1-Slot I/O Chassis with Integral Power Supply and Adapter 1771-AM1
  • 2-Slot I/O Chassis with Integral Power Supply and Adapter 1771-AM2
  • Direct Communication Module 1771-DCM
  • DL40 Dataliner 2706-xxxx
  • RediPANEL 2705-xxx
  • PanelView Terminal 2711-xxx
  • Remote I/O Adapter for 1336 AC Industrial Drives 1336-RIO
  • Remote I/O Adapter for 1395 AC Industrial Drives

Block Transfers with the 1756-DHRIO

The 1756-DHRIO modules support sending block transfer (BT) data and discrete I/O to the ControlLogix controller. This data exchange transfers up to 64 words of data to/from a selected I/O module.

The BT data exchange is message-based (that is, a message instruction in the Ladder Logic program of the ControlLogix controller must be used to initiate the BT request). In the case of digital I/O modules, simply by entering the adapter in the ControlLogix controller organizer, data is transferred without requiring instructions.

To send DH+ ‘Pass-Through’ messages to a 1756-DHRIO module, the module must be configured with a routing table, even if the channels are configured for remote I/O.

The process for completing block transfers on remote I/O remains consistent with all adapter products. The remote I/O network characteristics defined for the PLC-5 remote I/O scanner are the same for the 1756-DHRIO remote I/O scanner.

The message timeout for the BT message is fixed at 4.5 seconds. This timeout is a ControlLogix network response timeout associated with the connection established between the 1756-DHRIO module and the ControlLogix controller. The primary timeout for the BT response is remote I/O network based. This timeout occurs in 4 seconds if the I/O module fails to respond to the BT message.

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