PIC – ch. 2b

Move to GPR

• Move [copy] contents of WREG GPR/RAM

MOVLW 99H ;WREG=99HMOVWF 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?

ADDWF• 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

Or,

• ADDWF fileReg, w ; =[WREG] + [fileReg]

; destination of the result is WREG

• ADDWF fileReg, f ; =[WREG] + [fileReg]

; destination of the result is fileReg

Q. How to clear WREG?

MOVLW 0

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• ADDWF 12h, F ;add WREG to loc 12h• ADDWF 12h, F ;add WREG to loc 12h• ADDWF 12h, F ;add WREG to loc 12h

• Loc 12h 22 44 66 88• WREG 22 22 22 22

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• ADDWF 12h, w ;add WREG to loc 12h• ADDWF 12h, w ;add WREG to loc 12h• ADDWF 12h, w ;add WREG to loc 12h

• Loc 12h 22 22 22 22• WREG 22 44 66 88

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

Table 2.3File 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

• MOVF -move fileReg• NEGF-negative f• Rotate right, rotate left• SWAPF -swap nipples in fileReg• BTG -bit toggle fileReg

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

• C – carry• DC – digital carry• Z – zero • OV – overflow• N – negative

C

• It is affected after an 8-bit addition or subtraction, for unsigned arithmetic

• Ch. 5

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.

Z

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

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

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

• 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

Q. Status of C, DC, Z after addition of 38h and 2Fh for -

• MOVLW 38H• ADDLW 2FH

=========38h 0011 10002Fh 0010 1111-----------------------------67h 0110 0111 WREG = 67h

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

Q?

• MOVLW 9Ch• ADDLW 64h

• C = 1• DC = 1• Z= 1

• See Table 2.4

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

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