The Allen-Bradley 1772-LG control module is a processor control module that is made for the Allen-Bradley PLC-2/30 programmable controllers. The PLC-2/30 controller system consists of the 1771-LP3 processor and an I/O structure which is an I/O chassis that contains I/O modules. When used in combination with the I/O module and a user written program, the PLC-2/30 programmable controller can be used for numerous industrial applications, include process control, palletizing, material handling, pollution control/monitoring, and measurement and gauging applications. The 1772-LP3 processor contains a CMOS memory unit (read/write) that is used for storing program instructions, I/O status updates, and numeric values. The user-written program contains instructions that detail the operations that need to be performed. This program is entered from an Allen-Bradley 1770-T3 or a 17840-T50 terminal.

During program execution, the PLC-2/30 processor monitors input devices and energizes or de-energizes output devices based on the user program instructions. The user program can be altered according to the requirements of an application because the memory is programmable. The data table capacity for the 1772-LP3 processor can be increased to 8192 words with a 16 K memory or to 8064 words with an 8 K memory. When the local I/O racks are powered by the 1771-P3, 1771-P4, 1771-P5, or 1771-P7 power supplies, the 1772-LG module may experience problems with the racks. Processors in a TEST or RUN mode try to read local racks after recovering from a power lock. This may lead to a processor fault in the 1772-LG module. If a problem does occur, then the processor should be power cycled or the keyswitch should be put in the program load position and then returned to the RUN mode.