The Allen-Bradley 1775L1B is the main processor module for the PLC-3 system. Allen Bradley PLC-3 systems are composed of various modules that including communication modules, memory modules, scanners, power supplies, and main processors, such as this 1775L1B level 1 processor. This model is based on an AMD microprocessor and is used in PLC-3 systems to run cyclical program execution and perform memory management. This PLC-3 main processor module resides in two slots in the processor chassis (users should use the left-most slots in the chassis for this processor). In a multi-chassis PLC-3 system, the main processor module (in this case, the 1775L1B) is always located in chassis number 0. This module communicates and receives power through the PLC-3 chassis backplane. The 1775-L1B processor module uses the “level 1” instruction set that includes a relay type (8 instructions), a timer and a counter (7 instructions), arithmetic abilities (6 instructions), logical abilities (8 instructions), comparison abilities (8 instructions), data transfer abilities (7 instructions), shift register abilities (2 instructions), program control abilities (5 instructions),  and communication and diagnostic abilities (3 instructions). To remain effective in program execution, the 1775L1B processor module uses bit-slice microprocessors (AMD 2903), maintains an onboard I/O image table for high-speed I/O processing, and quickly determines the outputs states, using an advanced program scanning technique.

This module features multiple instruction types, a completely flexible data table, a high-speed program scan, a real-time interrupt routine, a programmable fault response, multiple contexts, a real-time clock and calendar, and diagnostic indicators. The main processor splits its memory into various dedicated and expendable areas, namely system status, system pointers, system symbols, module status, data table, force table, user program, and messages. This type of memory arrangement permits the user to easily increase the memory size while the application expands. The current requirements of the Allen-Bradley 1775L1B module are 9.4 A at 5 Volts DC and 40 mA at 15 Volts DC. This module’s operating temperature range is 0 to 60 degrees Celsius (32 to 140 degrees Fahrenheit)