This set of instructions has to do with the mathematic functions provided with for the PIC.

Now, let's see the instructions one by one:

With this instruction, you add the contents of the W register with a literal 8-bit value. The result is stored back to the W register. The status that may be affected from this instruction are:

• C - Carry
• DC - Digit Carry
• Z - Zero

The mathematic operation performed is:

• W = W + k
  Where 0 <= k <= 255

        movlw d'100'   ;The W register has now the decimal value '100'
        addlw d'50'    ;The decimal value '50' is added to the W register.
                       ;Now the W registe
r has the decimal value '150'

With this instruction, you add the contents of the W register with the contents of a file register. If d is 0 the result is stored in the W register, if d is 1 the result is stored back to the file register 'f'. The status that may be affected from this instruction are:

• C - Carry
• DC - Digit Carry
• Z - Zero

The mathematic operation performed is:

• Destination (d) = W + f
  Where 0 <= f <= 127

;This example requires that you have declare a file register for example
;TempRegister          equ 0x20
        movlw d'100'         ;The W register has the value '100'
        movwf TempRegister   ;The TempRegister has now the value '100'
        movlw d'50'          ;The W register has the value '50'
        addwf TempRegister,1 ;The values of W and TempRegister are added
                             ;and the result (150) is stored to TempRegister

With this instruction, you subtract the content of W register from a literal value. The result is stored back to the W register. The status that may be affected from this instruction are:

• C - Carry
• DC - Digit Carry
• Z - Zero

The mathematic operation performed is:

• W = k - W
  Where 0 <= k <= 255

        movlw d'30'   ;The W register has now the value '30'
        sublw d'100'  ;The content of W register is subtracted from the value '100'
                      ;Now the W register has the decimal value '70'

With this instruction, you subtract the contents of the W register from the contents of a file register. If d is 0 the result is stored in the W register, if d is 1 the result is stored back to the file register 'f'. The status that may be affected from this instruction are:

• C - Carry
• DC - Digit Carry
• Z - Zero

The mathematic operation performed is:

• Destination (d) = f - W
  Where 0 <= f <= 127

;This example requires that you have declare a file register for example
;TempRegister          equ 0x20
        movlw d'100'         ;The W register has the value '100'
        movwf TempRegister   ;The TempRegister has now the value '100'
        movlw d'30'          ;The W register has the value '30'
        subwf TempRegister,1 ;The value of W is subtracted from TempRegister 
                             ;and the result (70) is stored back to TempRegister

Many times you need to know if the result from a subtraction, using the sublw or the subwf instruction, is positive, zero or negative. This can be achieved by watching the Carry (C) and the Zero (Z) status:

With this instruction, you complement the contents of a file register. If d is 0 the result is stored in the W register, if d is 1 the result is stored back to the file register 'f'. The status that may be affected from this instruction are:

• Z - Zero

The mathematic operation performed is:

• Destination (d) = .NOT. f
  Where 0 <= f <= 127

;This example requires that you have declare a file register for example
;TempRegister          equ 0x20
        movlw b'11000101'    ;The W register has the value '11000101'
        movwf TempRegister   ;The TempRegister has now the value '11000101'
        comf TempRegister,1  ;The values of TempRegister is complimented
                             ;and the result (00111010) is stored to TempRegister

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Basics       What will you need       Choosing the right PICThe MPLAB       Getting familiar with the MPLAB environment       Creating a new project       Open and close projects       Creating new files and including them in the project       Your very first assembly program       Compile a program and transfer to the PICSection 1: Beginner's theoryMemory Organization       The Data Memory Organization       The Program Memory OrganizationThe instructions       General knowledge about instructions       Value Loading Instructions       Program Flow Instructions       Mathematic Instructions       Logic Function Instructions       Bit Orientated Instructions       Byte Orientated Instructions       Miscellaneous InstructionsThe Basic Special Function Registers       The Status Register       The Option_Reg Register       The TRIS and PORT registersBeginner's PIC Tutorials       How to use our PIC Tutorials       A Pushbutton turning an LED on and off       A Simple LED Flasher       Interfacing Multiple Switches - The internal Pull-Up resistors       An LED Sequencer       Interface a Single 7seg Digit       Interface Multiple 7seg Digits       A 3-digits Decimal Counter       A Clever ButtonSection 2: Intermediate theory       Instruction Cycle Duration and Calculated Delays       The Timer Modules - Timer0       The Timer Modules - Timer1       The Timer Modules-Timer2

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