1. PIC – ch. 2b
Md. Atiqur Rahman Ahad

2. Q: Can literal values directly into SFR?
Move to GPR
Move [copy] contents of WREG GPR/RAM
MOVLW 99H ;WREG=99H
MOVWF 0H
;move [copy] WREG contents to location 0h …
Cant move literal [immediate] values directly into the general-purpose RAM locations in the PIC18.
They must be moved there via WREG.
Q: Can literal values directly into SFR?

3. ADDWF ADDWF fileReg, D ; =[WREG] + [fileReg] Sources:
ADDLW 15H ; =15h + [WREG]
ADDWF fileReg, D ; =[WREG] + [fileReg]
Sources:
Content of WREG
fileReg: Content of file register (special or general)
Destination: D  indicates destination bit
If D = 0, destination of the result is WREG, or
If D = 1, destination is file register

4. Or, ADDWF fileReg, w ; =[WREG] + [fileReg]
; destination of the result is WREG
ADDWF fileReg, f ; =[WREG] + [fileReg]
; destination of the result is fileReg

5. Q. How to clear WREG?  MOVLW 0
HW: Find all other options.

6. Q. State the contents of file reg. RAM locations 12H and WREG after…
MOVLW 0 ;WREG = 0
MOVWF 12H ;move WREG to location 12 to clear it
MOVLW 22h ;WREG=22
ADDWF 12h, F ;add WREG to loc 12h
Loc 12h 
WREG 

7. Q. State the contents of file reg. RAM locations 12H and WREG after…
MOVLW 0 ;WREG = 0
MOVWF 12H ;move WREG to location 12 to clear it
MOVLW 22h ;WREG=22
ADDWF 12h, w ;add WREG to loc 12h
Loc 12h 
WREG 

8. Table 2.2 ALU instructions – using both WREG & fileReg
ADDWF fileReg, d ; d =W / d =F default is F
ADDWFC fileReg, d ;… with carry
ANDWF - AND
IORWF - OR
XORWF - Ex-OR w with f
SUBFWB - subtract f from w with borrow
SUBWF - subtract w from f
SUBWFB - subtract w from f with borrow

9. COMF fileReg, d ; -complement/invert f DECF -dec f
Table 2.3 File Reg. instructions – using fileReg or WREG as destination
COMF fileReg, d ; -complement/invert f
DECF -dec f
DECFSZ -dec f & skip if zero
DECFSNZ -dec f & skip if not zero
INC -inc f

10. MOVF -move fileReg
NEGF -negative f
Rotate right, rotate left
SWAPF -swap nibbles in fileReg
BTG -bit toggle fileReg

11. 2.4 PIC Status Flag Register
The STATUS register is of most importance to programming the PIC, it contains the arithmetic status of the ALU (Arithmetic Logic Unit), the RESET status and the bank select bit for data memory.
8-bit register
Only 5 bits to use by PIC18
Other 3 bits – not used and read as 0

12. C – carry
DC – digital carry
Z – zero
OV – overflow
N – negative

13. C
It is affected after an 8-bit addition or subtraction, for unsigned arithmetic
Ch. 5

14. DC – digital carry / Auxiliary carry flag
For BCD [binary coded decimal] arithmetic.
When there is a carry from bit-3 to bit-4 during an ADD or SUB – it is set, else, cleared.

15. Z If the result is zero, then Z= 1 Used in arithmetic or logic ops.
Z for looping
Ch. 3

16. OV – overflow flag
OV = 1, when the result of a signed number operation is too large, causing the high-order bit to overflow into the sign bit.
For signed arithmetic  OV, N
For unsigned arithmetic  C

17. N – negative flag For signed no., bit-7 as the sign bit.
If bit-7 = 0  Z=0 result is positive
If bit-7 = 1  Z=1 result is negative
Ch. 5

18. Some instructions affect all flags
E.g., ADDWL
Some inst. – only Z or N flag bits, or both
E.g., ANDWL
Some inst. – no flags at all!
E.g., all move instructions, except MOVF

19. Q. Status of C, DC, Z after addition of 38h and 2Fh for -
MOVLW 38H
ADDLW 2FH
=========
38h 
2Fh 
67h  WREG = 67h

20. C = 0 no carry beyond bit#7
DC = 1 carry from b#3 to b#4
Z = 0 WREG has a value not zero

21. Q?
MOVLW 9Ch
ADDLW 64h
C = 1
DC = 1
Z= 1

22. Conditional branch [jump]
Instructions Action
BC branch if C = 1
BNC branch if C != 0
BZ branch if Z = 1
BNZ branch if Z != 0
BN branch if N = 1
BNC branch if N != 0
BOV branch if OV = 1
BNOV
More – ch.3
See Table 2.4

24. 2.5 PIC Data formats
Numbers can be
Hex
Binary
Decimal
ASCII formats

25. 4 ways to show HEX numbers –
34h, 23H
0x23, 0X34
Nothing, just the value: 23, 45
h‘45’
E4h – x 0E4h – ok!
0F – ok! 0F = 0Fh

26. B’ ’
b’ ’
D’45’
d’56’
.67
A’2’
A’9’
To define ASCII strings [more than one character], use DB (define byte) directive.

27. EQU – equate EQU  To assign fixed data
SFR address [SFR – special-function reg.] & GPR
COUNT EQU 0x25
… …
MOVLW COUNT ;WREG = 25h

28. ORG – origin
ODG directive is used to indicate the beginning of the address.
ORG must be in hex
END directive
Last line of the PIC program.
#include
Tells the assembler to use the libraries…

29. radix dec radix directive Label: To indicate the numbering system
Hex? – by default
Decimal?
radix dec
Numbers will be considered as decimal
Label:
1st character must be an alphabetic char.
1st char – NOT number …

30. 2.7 PIC prog – assembling & linking
Source file - *.asm
ASM file is fed to the PIC assembler
It converts codes into machine code
Produce object file - *.o, error file *.err
Linking –
*.hex file
List file - *.lst
Map file - *.map
Debug file - *.cod
After a successful link – hex file is ready to be burned into the PIC’s program ROM and is downloaded into the PIC Trainers.

31. Little endian vs. big endian
LE – Low byte goes to low memory & high byte goes to the high mem. address
E.g., all Intel microprocessors …

32. 2.9 RISC Q. How to increase the processing power of a CPU?
Increase the clock frequency of the chip.
Higher the frequency, the more power & dissipation
Use Harvard architecture – increase the no. of buses to bring more info (code & data)
PIC18 has Harvard acrchi.
Change internal architecture of the CPU & use RISC architecture

33. RISC or CISC? RISC – reduced CISC – complex
RISC processors have fixed instruction size
1, 2, or even 3 bytes
Large no. of registers – at least 32 reg.
Large no. registers can avoid the need for a large stack to store parameters
Small instruction set.
Less instruc. – difficult for programmers!
Large programs.
Need more memory – but memory is cheap now!
PIC16 has 35 instructions
PIC18 has 75 instructions
CISC – Complete/Complex instr. Set computer!
- Not all instrc. are used n not often too.!