Registers and counters

Abstract

The operation of most digital systems involves the movement of information: taking it from one place, modifying it, and then sending it to the next stage of the process. To accomplish this, the information has to be stored in a way which is accessible by the circuit performing the modification. This temporary storage is provided by registers which are constructed from the latches and flip-flops described in Chapter 4. In a typical computer instruction, an ADD cycle is used here as an example, information in the form of a data word is read from the computer’s memory and stored in one register (the memory buffer register); this is then added to a word already stored in another register (the accumulator register) and the result is stored back in the accumulator register; from there it is written into a selected location in the memory. Temporary storage of data in registers and the transfer of data between registers is, therefore, a vital component of the operation of most systems.