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PI18… Ch. 3.1

PI18… Ch. 3.1. Md. Atiqur Rahman Ahad http://aa.binbd.com. 3.1 Branch - Loop. 2 ways to loop in PIC. DECFSZ  decrement fileReg ,  skip next instruction if 0 DEC F SZ fileReg , d Place GOTO target right below it to create a loop. AGAINX ADDLW 3 | | DECFSZ COUNTX

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PI18… Ch. 3.1

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  1. PI18…Ch. 3.1 Md. Atiqur Rahman Ahad http://aa.binbd.com

  2. 3.1 Branch - Loop • 2 ways to loop in PIC. • DECFSZ  decrement fileReg,  skip next instruction if 0 DECFSZ fileReg, d • Place GOTO target right below it to create a loop

  3. AGAINX ADDLW 3 | | DECFSZ COUNTX GOTOAGAINX

  4. Do Exa. 3.1 Add 3 to WREG – ten times. Place the result in SFR of PORTB.

  5. COUNTX EQU 0x25 ; Use location 25h for counter COUNTX MOVLW d’10’; WREG=10 [d=decimal] for counter MOVWF COUNTX; count, COUNTX = 10 MOVLW 0 ;clear WREG to 0. WREG = 0 now AGAINX ADDLW 3 ;sum, WREG = 3, then added up… DECFSZ COUNTX, F ;F, not W. If ‘W’, value to WREG GOTOAGAINX;repeat – until COUNTX becomes 0 MOVWF PORTB ;send sum/result to PORTB SFR

  6. 2 ways to loop in PIC. • DECFSZ • BNZ - branch if not zero - from PIC18… PIC16 has no BNZ

  7. AGAINX ADDLW 3 ;sum, WREG = 3, then added up… DECFSZ COUNTX, F ;F, not W. If ‘W’, value to WREG GOTOAGAINX;repeat – until COUNTX becomes 0 AGAINX ADDLW 3;sum, WREG = 3, then added up… DECF COUNTX, F ;decrement counter ; decrement fileReg. Z=1 [zero flag] if fileReg = 0 BNZAGAINX;branch/jump to AGAINX if Z=0

  8. Q. What is the max. number of times that the loop in Exa. 3.1/3.2 can be repeated?  Location COUNTX in fileRegis an 8-bit register. • It can hold max. of FFh / 1111 1111b / 255 decimal • So, it can be repeated max. of 255 times.

  9. Q. How to repeat 255++ times? Think about C prog. for (…){ … for (…){ … } } • Nestedloop of 2/3/… times. • ENDLESS? Time cost or complexity [of ur algorithm] . • O(n2), O(nlogn), O(n3), …

  10. Read other conditional jumps • BC - branch if C=1 • BNC … if no carry, / C=0 • BZ …if Z= 1 • BNZ • Etc. …

  11. All conditional jumps are short jumps • The address of the target must be within 256 bytes of the contents of the program counter (PC). • Read – unconditional long jumps • GOTO • Branch

  12. Function / subroutine • CALL - long call • RECALL - relative call • What is User-definedfunction? [think C prog] • Why do we use User-defined function?

  13. Stack – LIFO? FIFO? • Pop / Push Instructions … … CALL UserDefinedFunction;call of a subroutine Instructions … ------------------------------------------------------------- UserDefinedFunctionInstruction ;start of the subroutine Instruction … RETURN ;finishof the subroutine ;return to caller

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