Hierarchical specification and switch-level simulation of digital circuits

A software system for structured schematic documentation and switch-level simulation of digital integrated circuits is presented. By means of an interactive command language, the user can specify the schematic diagrams which document the actual digital design directly onto a graphical screen. This documentation can be performed hierarchically, in a manner where selected subcircuits are represented by macro symbols instead of all the relevant schematic primitives. This ensures a clear overview of even very complex designs. In addition to this schematic editor, the software system contains a translator which is able to convert the schematic documentation into an electrical specification of the actual design. This specification is the basis for an event-driven switch-level simulation algorithm which is able to calculate very rapidly the behaviour of the actual circuit and to submit warnings when critical races or hazard phenomena are detected. Experiments show that digital circuits, consisting of many thousand digital gates, can be specified and analysed on a mainframe computer during an interactive man-machine dialogue which normally requires a few hours of manual effort and a few minutes of CPU time.