Microprocessor control circuit with inverted reset and extendable runtime

Abstract

A microprocessor-based burner control apparatus for use in preventing incorrect ignition signals. An inverting circuit inverts and limits the magnitude of a periodic input supply voltage to create an activating signal. This activating signal is applied to the reset terminal of the microprocessor, which enters an active state during the logic high level of the activating signal and enters an inactive state during the logic low level of the activating signal. The processor is connected to the output circuits, which can only be operated during the positive half-cycle of the input supply voltage. During initial operation of the system, the microprocessor is only active during the negative half-cycle, at which time the outputs cannot be activated. The microprocessor then performs a series of tests on the system, and if all the tests are passed, the microprocessor generates an output signal. This output signal is applied to the reset terminal of the microprocessor, where it combines with the activating signal to form an override signal. The override signal allows the microprocessor to extend its active state into the positive half-cycle and operate the output circuits. The extended active state of the microprocessor also allows for better control of the output circuits due to the increase in processing time during each cycle of the input supply voltage.