Hcmarc-0ct
The Hcmarc-0ct communication module is produced by B&R Automation and belongs to the HCM Maestro PLC Modules series. Installed in a controller rack, it serves as the network interface that links multiple PLC nodes so distributed I/O racks, operator panels, or motion axes can exchange deterministic data across an ARCNET fieldbus. This arrangement lets one controller coordinate status and command traffic across several devices without separate point-to-point links. Because it is dedicated to fieldbus communication, the module handles network exchange separately from local control execution inside the rack.
The module transmits user data at a maximum rate of 2.5 MBaud, and access to the medium is organized by the Token Passing (ISO 802.4) method, which provides collision-free arbitration and predictable timing for cyclic control tasks. This predictable access method is useful where periodic updates must arrive in order and within a known cycle time. Communication follows the ARCNET protocol, which assigns each station a unique eight-bit address for orderly participation on the network. When coaxial cabling is used, one segment may run up to 300 m and support 8 stations; the required cable impedance is 93 Ω to reduce signal reflection at the BNC terminations. Twisted-pair wiring is also supported, with each segment limited to 120 m and ten devices, which allows flexible routing in plant layouts without repeaters.
A complete ARCNET loop can accommodate 255 logical nodes, which supports large installations that combine drive controllers, HMI panels, and safety processors on the same network. If coaxial amplifiers are inserted, the physical separation between the two most distant stations can reach 6 km, which is useful for conveyor lines or distributed pumping stations spread across large facilities. The available distance and node capacity make the module practical for machine groups that are spread across production areas rather than concentrated in one cabinet. Network layout still needs to follow the stated segment and media limits so token circulation remains predictable and every node has regular access to the bus.
