Allen Bradley PLC networks

There are different PLC networks used to connect devices to an Allen Bradley system, Data Highways and Control Net. Data highways are DH, DH+, DH 485.


  • DH is a local area network

  • Maximum number of devices can be connected: 64

  • DH link implements peer-to-peer communication through a scheme called floating master to provide each node equal access to become the master

  • A DH transmit 57.6K bits of data per second.

DH+ :

  • DH+ link is similar to the DH link, the only difference is that in the number of nodes, where the maximum number of allowed nodes are 15.

  • Maximum number of allowable devices are 64

  • Speed of data transmit ranges from 57.6, 115.2, or 230.4K bits per second.

  • DH+ is also implemented a peer-to-peer communication


  • DH485 is a peer-to-peer programming data acquisition link with 32nodes.

  • Here peer-to-peer communication uses a token-passing scheme to rotate link master among the nodes.

  • DH 485 Network using AIC+

Control Net:

  • The ControlNet network provides high-speed transmission of time-critical I/O and interlocking data and messaging data.

  • This data transfer capability enhances I/O performance and peer-to-peer communication in any system or application

  • The ControlNet network is highly deterministic and repeatable and remains unaffected as devices are connected or disconnected from it.