Abstract: A timeout mechanism for a computer system is provided, comprising a clocked linear feedback shift register and a programmable comparing mechanism. The linear feedback shift register comprises a series of latches serially connected to each other, and is responsive to a received interrupt signal to (i) incrementally count sequentially in the presence of the interrupt signal to provide a distinct binary vector array at the outputs of the latches for each count in the sequence and (ii) reset to a particular binary vector array in the absence of the interrupt signal. The comparing mechanism outputs a timeout command in response to the linear feedback shift register reaching a predetermined count and outputting a corresponding predetermined binary vector array at the output of the latches. The timeout mechanism uses a minimal amount of combinatorial logic, while permitting the issuance of a timeout command after the detection of an interrupt signal after any multiple of clock cycles.

Abstract: A parallel port interface for utilization between a first device and a second device designated by a user for transmitting a digital signal from the device to the second device. The parallel port interface includes a switchable driver circuit for transmitting the digital signal, which includes a first circuit for emulating an open collector circuit and a second circuit for emulating a totem pole circuit. The switchable driver circuit is controlled by a logic control circuit that automatically selects either the first circuit or the second circuit for transmitting the digital signal in response to the digital signal and a designation of the second device.