Logic of Controlled Threshold Devices

摘要

The synthesis of threshold logic circuits from several points of view is presented. The first approach is applicable to resistor-transistor networks in which the outputs are tied to a common collector resistor. In general, fewer threshold logic gates than NOR gates connected to a common collector resistor are required. Synthesis techniques based upon the use of Boolean matrices are presented. In this case the goal of the synthesis is a network to realize a specified function such that the failure of any but the output gate can be compensated for by a change in the threshold level (and possibly changes in the weights of the inputs). In general, the ability to compensate for a failure requires the synthesis of a network with more gates than if no compensation were required. The net result is that the synthesis is an involved procedure. A mechanism for changing weights of threshold gates using a photo-diode matrix is presented. The design of the control system for an IBM type 350 disc file is presented as an illustration of the design of a practical system in which threshold logic is employed. The function of the control system is to position the read-write heads over the specified track of a specified disc to read in or to read out data. Less logic circuitry is required if threshold logic rather than NOR logic is used. (Author)