Another very interesting set of instructions is the ones that have to do with the bits of a byte. The 16F88 is an 8-bit micro controller. This means that each byte will have 8 bits. Just to remind you that the most left bit is called MSB (Most Significant Bit) while the most right is called LSB (Less Significant Bit). Also, the numbering of the bits starts from zero base and counts form the LSB to the MSB. Thus, the LSB bit is the bit nmber 0 and the MSB is the bit number 7.

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

With this instructions you can set a bit within a register. The Status is not affected with this instruction. The 'b' can be a number from 0 to 7 corresponding to a bit position.

;This example requires that you have declare a file register for example
;TempRegister          equ 0x20
        bsf TempRegister,3     ;The bit in place 3 in register 'TempRegister' is SET (1)
        bsf PORTA,0            ;The bit in place 0 in register 'PORTA' is SET (1). If this
                               ;port pin is output, the corresponding pin will become HIGH

With this instructions you can clear a bit within a register. The Status is not affected with this instruction. The 'b' can be a number from 0 to 7 corresponding to a bit position.

;This example requires that you have declare a file register for example
;TempRegister          equ 0x20
        bcf TempRegister,3     ;The bit in place 3 in register 'TempRegister' is CLEARED (0)
        bcf PORTA,0            ;The bit in place 0 in register 'PORTA' is CLEARED (0). If this
                               ;port pin is output, the corresponding pin will become LOW

This instruction can be used for conditional execution of instructions. The two last lettes 'SS' stand for Skip if Set. The very next instruction after the BTFSS will be executed only if the bit 'b' withing register 'f' is NOT SET. Otherwise it will be replaced with a 'NOP' instruction and shall not be executed. The Status is not affected with this instruction. The 'b' can be a number from 0 to 7 corresponding to a bit position.

        btfss PORTA,4          ;Check bit '4' in register PORTA
        goto Bit_Was_Zero      ;If '0' goto Bit_Was_Zero
        .
        .

This instruction can be used for conditional execution of instructions. The two last lettes 'SC' stand for Skip if Clear. The very next instruction after the BTFSC will be executed only if the bit 'b' withing register 'f' is SET. Otherwise it will be replaced with a 'NOP' instruction and shall not be executed. The Status is not affected with this instruction. The 'b' can be a number from 0 to 7 corresponding to a bit position.

        btfsc PORTA,4          ;Check bit '4' in register PORTA
        goto Bit_Was_Zero      ;If '1' goto Bit_Was_Zero
        .
        .

This instruction is used to swap the nibbles of a register. When executed, the bits 0-3 will be swapped with the bits 4-7. 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 is not affected with this instruction.

;This example requires that you have declare a file register for example
;TempRegister          equ 0x20
        movlw b'11110000'      ;W has the binary number '11110000'
        movwf TempRegister     ;TempRegister has the binary number '11110000'
        swapf TempRegister,1   ;The nibbles in TempRegister are swaped
                               ;Now TempRegister has the value '00001111'

Previous page ---- Next page

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

Go back to the book contents

Go to the discussion forum of this book

Name   Email (shall not be published)   Website Notify me of new posts via email Write your comments below: BEFORE you post a comment:You are welcome to comment for corrections and suggestions on this page. But if you have questions please use the forum instead to post it. Thank you.