8020-SCP-311 is a Model 300, 512 Word Standard Processor with RAM that is manufactured by Square D. Each Model 300 processor is enclosed in a sheet metal steel case. This unit contains processor logic and memory for storing the user’s ladder diagram control program. The processor has two communications parts: one for programming and peripheral equipment, and one for inter-processor communications, access to a computer, or for a loader/monitor. There are three key modes on the processor: RUN, HALT, and DISABLE OUTPUTS. There are also five LED indicators on the processor: RUN, HALT, MEMORY, FORCE, and I/O.
When the RUN light is illuminated (green), the processor is operating on inputs and outputs and is scanning the ladder diagram program. When the RUN light is flashing, the processor is scanning the ladder diagram program but is not operating any I/Os. When the HALT light is illuminated or flashing (red), the processor is not scanning the ladder diagram program. When the MEMORY light is flashing (red), the processor has stopped due to a memory error. When the FORCE light is illuminated or flashing (red), one or more inputs and/or outputs have been forced to turn on or off, thereby overriding the ladder diagram program. When the I/O light is illuminated, there is a malfunction in the I/O system. This processor weighs 30 lbs. The logic is microprocessor-based. The memory size is varied in different processors. The memory utilization is 1 word per contact, coil, or branch.