DH+

Data Highway Plus, proprietary Allen-Bradley token-passing network for PLC-5 systems. This term is essential for understanding communication protocols in industrial automation and PLC programming.

In an industrial communication network, DH+ sits at the layer where deterministic data exchange between PLCs, drives, sensors, and HMIs has to happen reliably even when the plant floor is electrically noisy and the system needs to keep running for years without intervention. Data Highway Plus, proprietary Allen-Bradley token-passing network for PLC-5 systems.

Under the hood, DH+ is implemented at a specific position in the OSI model — typically physical, data-link, or application layer — and its behaviour determines whether downstream PLC scan cycles can stay deterministic. Engineers have to consider cycle-time impact, jitter, security, and brand support when comparing it against alternatives.

For practical work with DH+, the standard troubleshooting workflow is to verify the physical layer first (cabling, termination, voltage levels), then the addressing or message structure, then any timing or quality-of-service configuration. Vendors publish protocol-specific diagnostic tools that catch most issues quickly.