The Allen-Bradley 1756-CN2R is a ControlLogix communication module that is part of the Logix controller platform. This module is primarily used for establishing connectivity in redundant ControlNet network topology as it features Two (2) BNC ControlNet ports. This module occupies a single sot of the cassis and may be installed to any available slot of standard chassis such as 1756-A4, 1756-A7, 1756-A10, 1756-A13, 1756-A17 and used with standard ControlLogix power supply particularly 1756-PA72/C, 1756-PA75/B, 1756-PB72/C, 1756-PB75/B, 1756-PC75/B, 1756-PH75/B and redundant power supply such as 1756-PA75R, 1756-PB75R, 1756-PSCA2. ControlNet network is a multi-node communication network utilizing a coaxial cable trunk line with nodes connecting at the trunk line using drop cables. This particular module uses 1786-RG6 quad shield RG6 coaxial cable for connection to the network. Up to 5 Mbps transmission speed is supported by the 1756-CN2R. Aside from the dual ControlNet ports, the 1756-CN2R also comes with One (1) USB port that supports a 12 Mbps transmission rate at full speed. This port is mainly used for downloading module configuration, local connection firmware modification using the ControlFlash utility. It cannot be used for data communication purposes. This module is applicable for implementing Distributed I/O topology as it can cover up to 1000 meters per segment which can be easily extended with the use of repeaters as signal boosters for ControlNet segments longer than 1000 meters. It can be also to communicate with Human Machine Interface (HMI) devices and Supervisory Control and Data Acquisition (SCADA) systems. It supports up to 128 Logix connections and a maximum of 131 communication connections.

The 1756-CN2R ControlNet Connections per Communication Module by Allen-Bradley is a communication module attached to a slot on the ControlLogix Chassis that provides a ControlNet Network through the Common Industrial Protocol (CIP) and a peer-to-peer network for enhanced functions. It has a redundant configuration type and communicates at a rate of 5Mbps over a maximum of 99 nodes. The 1756-CN2R has a maximum of 128 Logix communication connections. It has a draw current of 1300mA at 5.1V DC and one of 3mA at 24V DC and it dissipates 6.6W heat at 22.5 BTU/hr. It has 30V DC isolation voltage with basic insulation tested at 500V for a minute between the ControlNet and the system. The 1756-CN2R has double ControlNet BNC, a ControlNet RJ45, and a single USB 1.1 port for connection and communication with other devices. It comes in an open enclosure type and is designated at the T4 IEC temperature code and at the T4A North American Temperature code. The 1756-CN2R operational temperature ranges between 0 and 60 deg. C (32 and 140 deg. F) at 5-95% non-condensing relative humidity, and it has an operational shock rate of 30G and a maximum vibration of 2G at 10-500Hz.