Interrupt Driven RS-232, Pulse Width Modulation, and Control Processing on a Single 8-bit PIC Chip

Report No. ARL-TR-4747
Authors: Justin Shumaker
Date/Pages: March 2009; 22 pages
Abstract: Autopilots utilizing a single processor allow for smaller, lighter, more cost-effective designs than those using multi-processor architecture. Presented here is a software architecture that allows multiple tasks to operate in a real-time mutually exclusive environment using a single 8-bit processor. This type of architecture will be utilized to create an autopilot using a single processor and sensors. The problem is preventing individual tasks from interfering with one another in a real-time environment. The processor selected for this design is the 8-bit microchip programmable integrated circuit (PIC) 18F2420. Hardware limitations on the microchip PIC, such as a lack of symmetric multi-processing, must be emulated in a round-robin interrupt scheduler whereby each task runs in sequence, receiving only a slice of the total processing time available.
Distribution: Approved for public release
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Last Update / Reviewed: March 1, 2009