Memory interface for the 2650 microprocessor

Abstract

The memory is an indispensible part of a microprocessor system and has a considerable influence on the system design. The type of memory to be used and the method of interfacing with the microprocessor must be chosen during the early design stages. This article describes a number of memory interface examples using the Signetics 2650 microprocessor. Detailed information about these memory systems can be found in the application notes of the 2650 microprocessor published by Signetics. There is an extensive choice of semiconductor memories: ROM, PROM, EPROM, RAM static and RAM dynamic. ROM can be used economically as program storage in systems which are produced in large quantities. PROM and EPROM are suitable as program storage in systems which are produced in small quantities. EPROM is especially attractive in the software development phase, or in systems where program changes are expected. RAM will generally be used as working storage. The capacity required is entirely dependent upon the application. For capacities lower than 4k bytes, static RAM may be used. For larger capacities, dynamic RAM is a more economical choice, although an extra memory refresh circuit is necessary. Three items must be considered for the interface design: • - logic level compatibility • - load and drive capability • - timing. The hardware requirement is greatly simplified by the high degree of compatibility between the microprocessor and memories.