The AB 1771-A2B is an I/O chassis for 1771 I/O modules. The 1771 PLC-5 system is a modular system that needs a 1771 I/O chassis to allow the installation of various modules. Communication between I/O modules and either the processor module or the I/O adapter module is provided by the backplane.

The 1771-A2B chassis has 8 I/O slots. It has a dimension of 12.4 x 14.0 x 7.6 in. and weighs 10.3 lbs. For installation in a 1771 PLC-5 system, it uses a back-panel mounting method with adequate spacing and open enclosure. The chassis backplane has a power supply of 8A at 5V DC.

The 1771-A2B chassis has a universal configuration for chassis mounting and system design because of its consistent design. 1771 I/O modules are small, flexible, cost-effective, and provide a complete range of digital, analog, and intelligent I/O modules for various applications. The I/O modules come with wiring arms and remote termination panels, eliminating the need to for disconnecting the wire to replace the module. For troubleshooting and diagnostics, status indicators are present on the front of modules. For future expansion, it can be easily replaced with a larger chassis. It is intended for use in an industrial environment with a 0 - 60 °C (32 - 140 °F) operating temperature, 5-95 % noncondensing relative humidity, and a 30g operating shock.