Switch-An Intelligent 256-Point Contact and Voltage Monitor for Computer Use

Contact sensing is an important part of any instrumentation and control computer. Contacts are often used to specify the state of a system. In implementing a contact sensor, there is a tradeoff made between a hardware design and a software design. This paper describes a computer peripheral device called SWITCH. It is a hardware implementation using random logic elements. Housed in a self-contained enclosure, this input device may be physically separated from the host computer using a 50-conductor transmission line for data transfers. SWITCH uses a simple control signal scheme to facilitate interfacing with a variety of computers. Included in the hardware is logic for single and repetitive scanning of all inputs and for host computer interrogation. By means of its most powerful feature, interrupt generation, SWITCH is able to relieve the host processor of much of the ``house keeping'' required by software implementations for computer contact sensing.