The 1771-A1B is an PLC-5 Chassis . The 1771-A1B chassis is the backbone of every PLC-5 programmable controller system. This chassis provides a communication path between various I/O modules and either the controller or the I/O adapter module. 1771-A1B is a universal and compact enclosure for the processor, power-supply modules, remote and extended-local I/O adapter modules, and I/O modules. 1771-A1B chassis has 4 slots for mounting various modules. The far-left slot of 1771-A1B chassis is reserved for either the processor or adapter module. The other slots in the chassis are compatible with communication modules, I/O modules, and power-supply modules. It is crucial to follow the compatibility tables for each PLC-5/1771 module. Please note the 1771-A1B is part of series B. Power supplies 1771-P1, -P2, -P7 and -PS7 can be mounted on the left side plate of the 1771-A1B chassis.

The 1771-A1B chassis is designed for panel mount installation. 1771-A1B chassis can receive power through processors with integral power supplies that provide 2 to 4 amps, power supply modules that provide 3 to 8 amps, and external power supplies that provide 6.5 to 16 amps. The largest back-plane current for the 1771-A1B is 16 amps operating at 5 Volts DC. The 1771-A1B chassis must be connected to a central ground bus via grounding studs situated on the chassis itself. The chassis’ power supply is configured via the configuration jumper. The jumper has two positions: "N" - position for external power supply, and "Y" - position for power-supply module or processor with and an integral power supply. 1771-A1B chassis cannot be powered with both a power-supply module and an external power supply at the same time.