Latches and Registers

Abstract

The combinational circuits introduced so far perform a function and, except for the ROM, do not provide any memory. The ROM provides a static memory, the content is predetermined. A system providing dynamic memory is required to store data which cannot be predetermined. Any two state (bistable) system which can be dynamically controlled will provide this function. Many systems acting in parallel can provide the required data width for operations provided by combinational circuits. The bistable systems are called latches and the parallel combination registers. Combinational circuits are free of loops. In this chapter we examine circuits with feedback loops. This is what allows them to store information. Propagation delays are important in the analysis of these circuits.