The development of processors for embedded system de-sign has essentially followed the development of microprocessors as a whole. The processor development has provided the process-ing heart for architecture which combined with the right software and hardware peripherals has become an embedded design. With the advent of better fabrication technology supporting higher transistor counts and lower power dissipation, the processor core has been integrated with peripherals and memory to provide standalone microcontrollers or integrated processors that only need the addition of external memory to provide a complete hardware system suitable for embedded design. The scope of this chapter is to explain the strengths and weaknesses of various architectures to provide a good understanding of the trade-offs involved in choosing and exploiting a processor family.
There are essentially four basic architecture types which are usually defined as 8 bit accumulator, 16/32 bit complex instruc-tion set computers (CISC), reduced instruction set computer (RISC) architectures and digital signal processors (DSP). Their develop-ment or to be more accurate, their availability to embedded system designers is chronological and tends to follow the same type of pattern as shown in the graph.
it should be remembered that in parallel with this life cycle, processor
architectures are being moved into microcontroller and integrated processor
devices so that the end of life really refers to the discontinuance of the
architecture as a separate CPU plus external memory and peripherals product.
The MC6800 processor is no longer used in discrete designs but there are over
200 MC6801/6805 and 68HC11 derivatives that essen-tially use the same basic
architecture and instruction set.