Allen-Bradley 1756-CN2/B ControlNet Communication Module

Configured for deterministic scheduled data exchange in ControlNet networks within ControlLogix automation systems, the Allen-Bradley 1756-CN2/B (1756-CN2/B communication module) provides direct network-level execution of controller-to-device communication over a 5 Mbps ControlNet medium.

Hardware Specifications

ControlNet Deterministic Scheduling and Redundant Media Operation

The 1756-CN2/B implements scheduled communication cycles on the ControlNet media layer, enforcing time-slot based data transmission between nodes. The module maintains fixed network scan timing at 5 Mbps, reducing variability in controller-to-device data exchange.

Dual BNC interfaces support redundant coaxial media paths. Media redundancy operates through continuous signal monitoring and automatic path selection, maintaining network continuity under single-channel degradation conditions. LED diagnostics provide real-time status of network traffic, node synchronization, and module state within the ControlLogix chassis backplane.

Frequently Asked Questions (FAQ)

Q: Does the 1756-CN2/B support hot-swap replacement in a powered ControlLogix chassis?
A: The module supports Removal and Insertion Under Power (RIUP) when installed in a compatible ControlLogix chassis slot. Network resynchronization occurs after reinsertion.

Q: What is the effect of backplane load on module operation?
A: The module draws approximately 1.0 A at 5.1 V DC from the chassis backplane. Excessive cumulative backplane loading across modules may affect system power budgeting.

Q: How does redundant media affect communication timing?
A: Dual BNC channels operate in parallel monitoring mode. Only one active path is used per scheduled transmission cycle, with automatic failover when signal integrity thresholds are violated.

Field Installation Guidelines

The module shall be installed in a dedicated ControlLogix chassis slot with all power removed or under RIUP-compliant conditions. Coaxial ControlNet cabling must be terminated with specified end-of-line resistors to maintain impedance matching across the network segment. Cable shielding must be bonded at designated grounding points to avoid differential noise injection.

Node addressing and network scheduling must be configured using RSNetWorx for ControlNet prior to runtime operation. Physical routing of BNC cabling shall avoid high-frequency drive lines and power conductors to reduce electromagnetic coupling effects. Chassis grounding shall follow ControlLogix system grounding architecture.