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![Structure of Assembly Language
• Series of lines
• Instruction
• Directives
• Consists of four fields
• [label] mnemonic [operands] [;commands]
• Label: refer to line by code (certain length)
• Mnemonic and operands are task that should be executed.
• Directive don’t generate any machine code and used by assembler](https://image.slidesharecdn.com/lec4introductiontopicassemblylanguageinstructionscontinued-220719182308-d1fe097c/85/Lec_4-Introduction-to-PIC-Assembly-Language-instructions-Continued-pdf-13-320.jpg)
Lec_4 Introduction to PIC Assembly Language instructions (Continued).pdf
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- 2. PIC STATUS REGISTER • To indicate arithmetic conditions • It is an 8 bit register •Five bits are used • D0: C Carry Flag • D1: DC Digital Carry Flag • D2: Z Zero Flag • D3: OV Overflow Flag • D4 N Negative Flag
- 7. Flag Bits and Decision Making Instruction Action BC Branch if carry BNCBranch if not carry BN Branch if negative BNN Branch if not negative BOV Branch if overflow BNOV Branch if not overflow BZ Branch if zero BNZ Branch if not zero
- 8. PIC DATA FORMAT and DIRECTIVES • There is one data type • 8 bits •It is the job of the programmer to break down data larger than 8 bits • Data type can be positive or negative • Data format are • HEX (default in PIC) 12 or 0x12 or H’12’ • Binary B’00010010’ • Decimal .12 or D’12’ • ASCII A’C’ or a’c’
- 9. Assembler Directives • The instruction tell the CPU what to do, while directives give direction to the assembler • Directives: EQU, SET, ORG (origin), END,LIST •EQU (equate) • It is used to define a constant value of a fixed address • It associates a constant number with a data or an address label so that when the label appears in the program, its constant will be substituted for the label • COUNT EQU 0x25 • … ….. ….. • MOVLW COUNT ;WREG 25H
- 10. • SET • It is used to define a constant or a fixed value •Identical to EQU but SET may be re-defined later • ORG (origin) • It is used to indicate the beginning of the address • END • This indicates to assembler the end of the source (asm) file • LIST • It indicates to the assembler the specific PIC chip for which the program should be assembled • LIST P=18F452
- 11. Rules for labels in Assembly Language • Unique name • Alphabetic letters •Upper, lower, digits (0-9), special char. (? . @ _ $) • The first letter muse be Alphabetic letters • Not a reserved word
- 12. Introduction to PIC Assembly Language • Difficult for us to deal with the machine code (0s and 1s) • Assembly language provide •Mnemonic: codes and abbreviations that are easy to remember • Faster programming and less prone error • LLL (why?) • Programmer must know all Reg…..etc • Assembler is used to translate the assembly code into machine code (object code)
- 13. Structure of Assembly Language • Series of lines • Instruction •Directives • Consists of four fields • [label] mnemonic [operands] [;commands] • Label: refer to line by code (certain length) • Mnemonic and operands are task that should be executed. • Directive don’t generate any machine code and used by assembler
- 14. Sample of Assembly Language Program SUM EQU 10H ;RAM loc 10H fro SUM ORG 0H; start at address 0 MOVLW 25H ; WREG = 25 ADDLW 0x34 ;add 34H to WREG=59H ADDLW 11H ;add 11H to WREG=6AH ADDLW D’18’ ; W = W+12H=7CH ADDLW 1CH ; W = W+1CH=98H ADDLW b’00000110’ ; W = W+6H=9EH MOVWF SUM ;save the result in SUM location HERE GOTO HERE ;stay here forever END ;end of asm source file
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