A Hard Programmable Control Unit Design Using VLSI Technology

Microprogramming has become a widely used technique which brings versatility to the control unit of a digital system. However, since all microcommands contained in a microinstruction are changed simultaneously, this form of control requires the coding of all possible combinations of parallel commands as separate microinstructions. This causes the resulting microprograms to become space- and timewise inefficient and makes it very difficult to control and/or synchronize independent processes. A new approach to modeling and implementing the flow of control in hardware systems is presented in this paper. Here a control flow is realized by a set of independent control operators that pass control to each other according to the precedence relationships defined by the control function which is implemented. The detailed architecture of a VLSI chip to implement a control unit as a hard- programmable control unit (HPCU) is also given. An HPCU contains many independent control operators and allows mask-programmable connections to be made among the operators to implement any given control function. Examples included in the paper demonstrate the effectiveness of an HPCU in implementing complex parallel control flows.