[Resolvido] Ajuda com instruções Assembly [pf]

WHILE alguma_coisa < 5

;instrucoes

ENDW

if - Begin Conditionally Assembled Code Block 

Syntax 

if expr

Description 

Begin execution of a conditional assembly block. If expr evaluates to true, the code immediately following the if will assemble. Otherwise, subsequent code is skipped until an else directive or an endif directive is encountered. 



An expression that evaluates to zero is considered logically FALSE. An expression that evaluates to any other value is considered logically TRUE. The if and while directives operate on the logical value of an expression. A relational TRUE expression is guaranteed to return a nonzero value, FALSE a value of zero. 



if's may be nested up to 16 deep. 



Usage 

This directive is not an instruction, but used to control how code is assembled, not how it behaves at run-time. Use this directive for conditional assembly or to check for a condition, such as to generate an error message. 



See Also 

else endif

Simple Example 

if version == 100; check current version

  movlw 0x0a

  movwf io_1

else

  movlw 0x01a

  movwf io_2

endif

Application Example - if/else/endif 

This program demonstrates the utility of if, else and endif assembly directives. 



  #include p16f877a.inc   ;Include standard header file

                          ;for the selected device.

  variable config         ;variable used to define

                          ;required configuration of

                          ;PORTA & PORTB, not to be confused

                          ;with __config.

  config set  .1          ;Set config to decimal .1

RST     CODE     0x0      ;The code section named RST

                          ;is placed at program memory

                          ;location 0x0. The next two

                          ;instructions are placed in

                          ;code section RST.

     pagesel  start       ;Jumps to the location labelled

     goto     start       ;'start'.

PGM     CODE              ;This is the begining of the

                          ;code section named PGM. It is

                          ;a relocatable code section

                          ;since no absolute address is

                          ;given along with directive CODE.

start

  banksel TRISA

  if config==0x0          ;If config==0x0 is true,

     clrw                 ;assemble the mnemonics up to

     movwf TRISA          ;the directive 'else'. Set up PORTA

     movlw 0xff           ;as output.

     movwf TRISB

  else

     clrw                 ;If config==0x0 is false,

     movwf TRISB          ;assemble the mnemonics up to

     movlw 0xff           ;the directive 'endif'. Set up PORTB

     movwf TRISA          ;as output.

  endif

  goto  $                 ;Go to current line (loop here)

  end

while - Perform Loop While Condition is True 

Syntax 

while expr

:

endw

Description 

The lines between the while and the endw are assembled as long as expr evaluates to TRUE. An expression that evaluates to zero is considered logically FALSE. An expression that evaluates to any other value is considered logically TRUE. A relational TRUE expression is guaranteed to return a non-zero value; FALSE a value of zero. 



A while loop can contain at most 100 lines and be repeated a maximum of 256 times. while loops can be nested up to 8 deep. 



Usage 

This directive is not an instruction, but used to control how code is assembled, not how it behaves at run-time. Use this directive for conditional assembly. 



See Also 

endw if

Simple Example 

while is not executed at run-time, but produces assembly code based on a condition. View the list file (*.lst) or disassembly window to see the results of this example. 



test_mac macro count

         variable i

i = 0

         while i < count

         movlw i

i += 1

         endw

         endm

start

         test_mac 5

         end

Application Example - while/endw 

This example shows the usefulness of directive while to perform a loop while a certain condition is true. This directive is used with the endw directive. 



  #include p16f877a.inc   ;Include standard header file

                          ;for the selected device.

  variable i              ;Define the symbol 'i' as a

                          ;variable.

mydata  udata 0x20        ;Allocate RAM for labels

  reg_hi res 1            ;reg_hi and reg_lo.

  reg_lo res 1

RST     CODE     0x0      ;The code section named RST

                          ;is placed at program memory

                          ;location 0x0. The next two

                          ;instructions are placed in

                          ;code section RST.

  pagesel  start          ;Jumps to the location labelled

  goto     start          ;'start'.

shift_right  macro  by_n  ;Beginning of a macro, which

                          ;shifts register data n times.

                          ;Code length generated after

                          ;assembly, varies depending upon

                          ;the value of parameter 'by_n'.

i=0                       ;Initialize variable i.

  while  i< by_n          ;Following 3 lines of assembly

                          ;code are repeated as long as

                          ;i< by_n.

Up to 100 lines of codes are allowed inside a while loop. 



  bcf    STATUS,C         ;Clear carry bit.

  rrf    reg_hi,F         ;reg_hi and reg_lo contains 

  rrf    reg_lo,F         ;16-bit data which is rotated

                          ;right through carry.

i+=1                      ;Increment loop counter i.

i cannot increment to more than 255 decimal. 



  endw                    ;End while loop. The loop will

                          ;break here after i=by_n.

  endm                    ;End of 'shift_right' macro.

PGM     CODE              ;This is the begining of the

                          ;code section named PGM. It is

                          ;a relocatable code section

                          ;since no absolute address is

                          ;given along with directive CODE.

start

   movlw   0x88           ;Initialize reg_hi and

   movwf   reg_hi         ;reg_lo for observation.

   movlw   0x44

   movwf   reg_lo

  shift_right  3          ;Shift right 3 times the 16-bit

                          ;data in reg_hi and reg_lo. This

                          ;is an example. A value 8 will

                          ;shift data 8 times. 

  goto  $                 ;Go to current line (loop here)

  end

A while loop can contain at most 100 lines and be repeated a maximum of 256 times. while loops can be nested up to 8 deep.

'[Daniel

;4831397']
Entao se eu colocar por ex.

WHILE alguma_coisa == 100

ele sai desse loop quando alguma_coisa for igual a 100, é isso?

Enquanto alguma_coisa for igual a 100

    ;execute o que está aqui dentro

Repita

'[Daniel

;4831397']
No caso da explicação do programa (ajuda) ele diz q so pode fazer o loop 255vezes, no maximo 8 pulos dentro dela e no maximo 100 linhas.

correto?

WHILE cond

    WHILE cond2

        WHILE cond3

            ;voce pode colocar ate 8 loops dentro de um loop

        ENDW

    ENDW

ENDW

Fergo disse:

Não, é o contrário. Ele vai sair do loop quando alguma coisa for diferente de 100. Talvez se você "ler" a linha traduzida para o portugues, fique mais fácil de visualizar. Traduzindo o seu código acima:

Enquanto alguma_coisa for igual a 100

    ;execute o que está aqui dentro

Repita

A condição que você coloca é aquela para ele continuar no loop, não para sair dele.

Fergo disse:

As duas primeiras, sim. A última, que fala "while loops can be nested up to 8 deep", indica que você pode encapsular (colocar um dentro do outro) o loop em 8 níveis. Por exemplo:

WHILE cond

    WHILE cond2

        WHILE cond3

            ;voce pode colocar ate 8 loops dentro de um loop

        ENDW

    ENDW

ENDW

Essas limitações estão relacionadas com a capacidade de processamento/armazenamento do PIC. Por exemplo, o fato de poder realizar o loop no máximo 256 vezes indica possivelmente que o incrementador utilizado para a contagem é de apenas 1 byte (0 a 255).

Fergo

 MOVF		reg1,W 

 XORWF		reg2,W

 BTFSC		STATUS,Z				;reg1=reg2?

 GOTO		vai_a_algum_lugar		;sim

 MOVF		reg2,W				;nao

 SUBWF		reg1,W				;reg1-reg2?

 BTFSS		STATUS,C

 GOTO               tal_linha

 GOTO               outra_linha