Understanding Microcontrollers: Architecture, Features, and Instruction Set Overview

1. Micro controllers • A self-contained system in which a processor, support, memory, and input/output (I/O) are all contained in a single package.

2. Types of Microcontrollers • Embeded (Self-contained) 8 bit • 16-32 bit • Digital Signal Processors

3. Basic Features • Processor reset • Device clocking • Central processor • Program and Variable Memory (RAM) • I/O pins • Instruction cycle timers

4. More Sophisticated Features • Built-in monitor/debugger program • Interrupt capability • Analog I/O (PWM and variable dc I/O • Serial I/O (synchronous, a synchronous) • Parallel I/O (including direct interface to a master processor • External memory interface

5. Processor Architecture • CISC • Large amount of instructions each carrying out a different permutation of the same operation • Functionality of the instructions is more dependent upon the processor’s designer

6. Processor Architecture • RISC • Fundamental set of instructions • More control for users to design their own operations

7. Processor Architecture • Princeton (Van Neumann) architecture • Common memory for program and data • Simple chip design • Execution of an instruction can take multiple cycles

8. Processor Architecture • Harvard architecture • Separate memory space program and data • Instructions are executed in one cycle • Easier timing of loops and delays

9. Processor Architecture • Princeton architecture example Mov acc, reg Cycle 1 Read instruction Cycle 2 Read data out of Ram and put into Acc

10. Processor Architecture • Harvard architecture example Mov acc, reg Cycle 1 Execute previous instruction Read “move acc, reg” Cycle 2 Execute “move acc, reg” instruction

11. Microchip PIC Micro controllers(PIC 16F877)

12. Hardware Architecture • PIC Microcontrollers have following main features: • Harvard Architecture • RISC Feature • CPU pipelines instruction fetching and execution in order to achieve an execution of one instruction at every cycle

15. Memory Organization • Program Memory • Register File Memory

16. Program Memory • Used for storing compiled code • Each location is 14 bits long • Every instruction is coded as a 14 bit word • Addresses H’000’ and H’004’ are treated in a special way • PC can address up to 8K addresses

19. Register File Memory • Consist of 2 Components • General Purpose Register (GPR) Files (RAM) • Special Purpose Register (SPR) files • This portion of memory is separated into banks of 128 bytes long

21. Register Addressing Modes • There are 3 types of addressing modes in PIC • Immediate Addressing • Movlw H’0F’ • Direct Addressing • Indirect Addressing

22. Direct Addressing • Uses 7 bits of 14 bit instruction to identify a register file address • 8th and 9th bit comes from RP0 and RP1 bits of STATUS register. • Exp: Z equ D’2’ btfss STATUS, Z

24. Indirect Addressing • Full 8 bit register address is written the special function register FSR • INDF is used to get the content of the address pointed by FSR • Exp : A sample program to clear RAM locations H’20’ – H’2F’ .

26. Some CPU Registers • STATUS • PC • W • PCL • PCLATH

28. Instruction Set • Every Instruction is coded in a 14 bit word • Each instruction takes one cycle to execute • Only 35 instructions to learn (RISC)

29. Instruction Set • Uses 7 bits of 14 bit instruction to identify register file address • For most instructions, W register is used as a source register • The result of an operation can be stored back to the W register or back to source register

31. Some Arithmetic Operations • addwf FSR, w ; Add w to FSR and put result in w • iorwf TMR0, f ; Inclusive OR w with TMR0 and store result in TMR0 • addwf reg ; Add content of the reg to content of the w and store the result back into reg (source)