Microcontrolers

Microcontrolers

1. There are 4 steps in the control unit: Program counter,instruction read, Decode i form this step there are 2 possiblities either execute or write back.

2. Important selection features:

   • -Word length-Clock Cycles -Clock frequency-Low-Power - Architecture

3. More History

   • First Microprocessor – Intel 4004 from the year 1971, it a pretty simple device compare to now a days.
     • First Microcontroller – TI TMS1000 first produced in 1974 witha clock rate of 4mHz
       • Typical features for Embedded Systems. – Clock rate: 100 MHz – Word length: 32 bits

4. Architecture

   • There are 2 basic architectures for microprocessors “Von Neumann”- Architecture – “Harvard” - Architecture
     • Von Neumann” it has shared memory space between code and data it has shared memory busses between code and data
     • “Harvard” it has two independent memory spaces for code and data and two memory bus systems for code and data

5. CISC/RISC

   • Complex Instruction Set Computer
     • It has an extensive and complex instructions sets, it was the favorite architecture from 1971to 1980
   • Reduced Instruction Set Compute
     • Favorite since 1980, the features are Single cycle instructions, one instruction per clock - CPI=1; Clock Cycle per Instruction (CPI) , uniform instructions , Load/Store architecture and high level languages.
   • Now a days architecures have the advantages of both CISC and RISC, these architectures are called Hybrid Architectures

6. Isolated vs Memory map

   • The characteristics of memory maps are I/O ports/registers appear as addresses on common bus with memory ,I/O ports that are accessed as though they are locations in memory ,Employed on the STM32 microcontrollers
   • The characteristics of Isolated maps are I/O ports/registers have separate control signals from those used with memory, Special instructions are used to access I/O ports/registers, Employed on Intel x86 processors