Basic Microprocessor Architecture and Interface :

Introduction:

Intel launches its first 4-bit microprocessor 4004 in the year 1971 and 8-bit microprocessor 8008 in the year 1972. These microprocessors could not carry on as general purpose microprocessors due to their and performance limitations and design. Launching of the first general purpose 8-bit microprocessor 8080 in the year 1974 by Intel is considered to  be  the  first  main  stepping   stone  towards  the development  of advanced  microprocessors. The microprocessor 8085 followed 8080, with a few more features included to its architecture, which resulted in a functionally full microprocessor.  The main restriction  of the 8-bit microprocessors  were their low speed of execution, low memory addressing capability, restricted  number of general purpose registers and a less powerful instruction set . All these restriction of the 8-bit microprocessors tempted the designers to go for more powerful processors in terms of advanced architecture, larger memory addressing capability, more processing capability, and a more powerful instruction set. The 8086 was a outcome of such developmental design efforts.

In the family of 16-bit microprocessors, Intel's 8086 was the first 1 launched in the year1978. The lancing of the 16-bit processor was a result of the increasing demand for more and more powerful and high speed computational resources.  8086 microprocessor has a much more powerful instruction set along with the architectural developments which imparted substantial programming improvement and flexibility in speed over the 8-bit microprocessors.

The peripheral chips designed earlier for 8085 were compatible with microprocessor 8086 with slight or no modifications. Although  there is a considerable  dissimilarity  between  the memory  addressing  techniques  of 8086  and  8085,  the  memory  interfacing  technique  is same,  but  includes  the  use of a few  additional signals.  The clock requirements are also different ascompared to 8085, but the wholeminimal system organization of 8086 is same to that of a general 8-bit microprocessor. In this chapter, the architectures of 8088 and 8086 are explained in enough details along with the interfacing of the supporting chips withthem to form a minimum system. The system organization is also explained in significant details for both the operating modes of 8088 and 8086, along with essential timing diagrams.