Data Highway Plus (DH+) Network

Data Highway Plus (DH+) Network: A Detailed Description

1. Introduction

2. Network Architecture

• Topology: The DH+ Network typically employs a token-passing bus topology. In this configuration, multiple devices are connected to a common bus or cable, forming a linear network structure. The token, which is a special control signal, circulates among the connected devices. Only the device that holds the token is allowed to transmit data onto the network at a given time. This mechanism helps to manage network access and avoid data collisions, ensuring orderly and reliable communication.
• Nodes and Devices: A wide variety of devices can act as nodes on the DH+ Network. These include programmable logic controllers (PLCs), human-machine interfaces (HMIs), remote I/O modules, and other intelligent devices used in industrial automation. Each node has a unique address assigned to it, allowing for identification and targeted communication within the network. The network can support a considerable number of nodes, depending on its configuration and the specific requirements of the application, enabling integration of multiple components in a single industrial system.

3. Communication Characteristics

• Data Transfer Rate: The DH+ Network offers a moderate data transfer rate that is well-suited for many industrial applications. It typically operates at speeds such as 57.6 kbps, which may seem relatively low compared to modern high-speed networks but is sufficient for transmitting the types of data commonly exchanged in factory floor automation, like sensor readings, control commands, and status updates between devices.
• Message Format: Data is transmitted in messages with a specific format defined by the DH+ protocol. These messages contain information such as the source address (identifying the sending device), the destination address (specifying the receiving device), and the actual data payload. The protocol also includes error-checking mechanisms, such as checksums or parity bits, to detect and correct any errors that may occur during transmission, ensuring the integrity of the communicated data.
• Communication Distance: It can cover reasonable distances within an industrial plant or factory environment. The maximum cable length for a single segment of the network usually depends on factors like the cable type and the baud rate used, but it can typically extend up to several hundred meters. In larger facilities, repeaters or bridges can be used to extend the network's reach and connect different segments together, allowing for broader coverage and connection of dispersed devices.