DH+ and DH485

DH+ (Data Highway Plus) and DH485 are industrial communication protocols developed by Allen-Bradley (now part of Rockwell Automation). These protocols are widely used for communication between programmable logic controllers (PLCs) and other industrial devices.

DH+ (Data Highway Plus)

DH+ is a proprietary communication protocol designed for high-speed, peer-to-peer communication between PLCs and other industrial devices. It operates over a coaxial cable or twisted pair and uses token-passing for network access control.

Key Features of DH+

• Network Topology: Supports both bus and star topologies.
• Speed: Typically operates at 57.6 kbps or 230.4 kbps.
• Addressing: Uses node addresses ranging from 0 to 77 octal (0-63 decimal).
• Media: Uses RG-6 coaxial cable or shielded twisted pair.

DH+ Pinout (3-Pin Phoenix Connector)

DH+ typically uses a 3-pin Phoenix connector for communication:

• Pin 1: Blue (Data A)
• Pin 2: Shield (Ground)
• Pin 3: Clear (Data B)

Example: Connecting PLCs via DH+

To connect multiple PLCs using DH+, follow these steps:

1. Connect the blue wire (Data A) to Pin 1 of each PLC.
2. Connect the shield wire (Ground) to Pin 2 of each PLC.
3. Connect the clear wire (Data B) to Pin 3 of each PLC.
4. Ensure proper termination at both ends of the network.

DH485 Protocol

DH485 is another proprietary communication protocol from Allen-Bradley, designed for industrial automation networks. It is a balanced transmission line standard, typically operating over twisted pair cables.

Key Features of DH485

• Network Topology: Supports bus topology.
• Speed: Operates at 19.2 kbps.
• Addressing: Uses node addresses ranging from 0 to 31.
• Media: Uses shielded twisted pair cable.

DH485 Pinout (6-Pin Phoenix Connector)

DH485 typically uses a 6-pin Phoenix connector for communication:

• Pin 1: Drain (Ground)
• Pin 2: Clear (Data A)
• Pin 3: Blue (Data B)
• Pin 4: No Connection
• Pin 5: No Connection
• Pin 6: Shield (Ground)

Example: Connecting PLCs via DH485

To connect multiple PLCs using DH485, follow these steps:

1. Connect the clear wire (Data A) to Pin 2 of each PLC.
2. Connect the blue wire (Data B) to Pin 3 of each PLC.
3. Connect the shield wire (Ground) to Pin 6 of each PLC.
4. Ensure proper termination at both ends of the network.