About the 8020-SCP-321
8020-SCP-321 is a Model 300, 512 Word Deluxe Processor with RAM that is manufactured by Square D. Only the portion of the ladder diagram program that is being utilized is scanned. The processor start-up sequence first requires the application of AC power. Then, a signal pulse turns off external outputs. The processor will perform a self-test, the I/O data will stabilize, and the I/O forcing memory is reset.
Further system initialization occurs if a local interface module is used. The input status is then updated, and if the key switch is in the DISABLE OUTPUTS or RUN position, the processor scans the user memory. The processor then continues scanning user memory setting outputs on or off according to the ladder diagram program in user memory. When powering down, the processor performs an orderly shutdown procedure.
When a device is attached to the Programmer port, that device has full access to the processor. Other processors and a CRT programmer may be connected to this port up to 10,000 feet away. A hand-held programmer may be connected to this port up to 6 feet away. A number of devices may be connected to the communications port, including printers, loaders/monitors, cartridge type loaders, SY/NET network interface modules, and other processors. Other processors may be daisy-chained together in order to expand operations. Connecting a loader/monitor allows for monitoring of the I/O status and register values, as well as displaying of alphanumeric messages. The loader monitor may be panel mounted within 10 feet of the processor.
