Assembly Language Instructions and Operators in PIC Microcontroller Programming, Slides of Assembly Language Programming

Download Assembly Language Instructions and Operators in PIC Microcontroller Programming and more Slides Assembly Language Programming in PDF only on Docsity!

ISA_Part1 1

Introduction to PIC Instruction Set Architecture Part I

• The Software

ISA_Part1 2

Organizational Issues

There should be place for the following:

1. Concept of registers
2. Instruction syntax and format - RISC
3. Immediates, constants, locals
4. Dissassembly, pseudo instructions, multiply and divide
5. Instruction timing
6. Memory addressing – direct, indirect, relative
7. Map “ifs” into conditional branching
8. Map inequalities into conditional branching
9. Use the keywords “bitwise” and “logical operators”

ISA_Part1 4

PIC Instruction Set Architecture ( Summary ) ° Machine Environment Target ° Instruction Categories  Load/Store  Computational W PC Registers Data

ISA_Part1 5

Harvard Architecture ° Data memory is separate from Program memory. ° (Intel et.al, have von Neumann integrated memory.) ° Allows data and program information to move separately and so is faster than von Neumann.

ISA_Part1 7

Review C Operators/operands

• Operators: +, - , *, /, % (mod); (7/4==1, 7%4==3)
• Operands:
  • Variables : fahr, celsius
  • Constants : 0 , 1000 , -17, 15.
• In C (and most High Level Languages) variables declared and given a type first  Example: int fahr, celsius; int a, b, c, d, e;

ISA_Part1 8

C Operators/operands

• This is the Computation Model by ``State- Effects''. Programs move from state to state by means of assignments changing their state
• Assignment Statement: Variable = expression, e.g. , celsius = 5*(fahr-32)/9; a = b+c+d-e;

ISA_Part1 10

Assembly Operators/instructions ° How to do the following C statement? a = b + c + d - e; ° Break into multiple instructions ° To right of semicolon (;) is a comment terminated by end of the line. Applies only to current line. ° C comments have format /* comment */ , can span many lines

movfw b ; Get the value of b in the register

addw c,w ; Add the value in b to the value in c and move to register

movwf a ; Store this first sum in a

mMovfw d ; Get the value of d into the register

addw a,f ; Add this new value to a

movfw e ; Get the value of e into the register

subwf a,f ; Subtract e from a and keep the value in location a.

ISA_Part1 11

Assembly Operators/instructions ° Note: Unlike C (and most other HLLs), each line of assembly contains at most one instruction add a,b,c add d,e,f WRONG add a,b,c add d,e,f RIGHT

ISA_Part1 13

Compilation -- Summary ° C statement (5 operands, 3 operators): f = (g + h) - (i + j); ° Becomes 3 assembly instructions (6 unique operands, 3 operators): ° In general, each line of C produces many assembly instructions One reason why people program in C vs. Assembly; fewer lines of code Other reasons? (many!)

movfw g ; Get the value of g in the register

addw h,w ; Add the value in g to the value in h and move to register

movwf f ; Store this first sum in a

movfw i ; Get the value of i into the register

subw f,f ; Add this new value to a

movfw j ; Get the value of e into the register

subwf f,f ; Subtract e from a and keep the value in location a.

ISA_Part1 14

These are the 35 instructions available on some PIC processors.

ISA_Part1 16

A Simple First Program The goal is to do a loop 256 times **org 0x Counter db 0 clrf Counter Loop: decfsz Counter goto Loop

---

----** New Instructions: clrf decfsz goto

ISA_Part1 17

New Instructions: clrf decfsz goto

ISA_Part1 19

New Instructions: clrf decfsz goto

ISA_Part1 20

New Instructions: clrf decfsz goto Related Instructions: clrw incfsz decf incf