1. Md. Atiqur Rahman Ahad http://aa.binbd.com
PIC18… Ch. 3.1
Md. Atiqur Rahman Ahad

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 GOTO AGAINX

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 GOTO AGAINX ;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…
COUNTX EQU 0x25 ; Use location 25h for counter COUNTX MOVLW d’10’ ; WREG=10 [d=decimal] for counter MOVWF COUNTX ; count, COUNTX = 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
GOTO AGAINX ;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
BNZ AGAINX ;branch/jump to AGAINX if Z=0

8. Q. Implement in Assembly lang.
- for(i=0; i<=10; i++)
- for(i=100; i>=0; i--)

9. Q. What is the max. number of times that the loop in Exa. 3. 1/3
Q. What is the max. number of times that the loop in Exa. 3.1/3.2 can be repeated?
 Location COUNTX in fileReg is an 8-bit register.
It can hold max. of FFh / b / 255 decimal
So, it can be repeated max. of 255 times. Why not 256??

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

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

12. 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

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

14. CALL UserDefinedFunction ;call of a subroutine
Stack – LIFO? FIFO?
Pop / Push
Instructions … …
CALL UserDefinedFunction ;call of a subroutine
UserDefinedFunction Instruction ;start of the subroutine
Instruction
RETURN ;finish of the subroutine
;return to caller