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ASSEMBLY LANGUAGE MPLAB PIC18f2550

I am trying to "AND" 2 Variables "If Variable_1 = 0 AND Variable_2 = 1 then" "DO WHAT IS NEEDED." "End If"

This below makes no sense used as a "AND" Logic Function. Will the above STATEMENT work using ANDWF or ANDLW? Do I need to ANDWF each Variable separately, or is it possible to use something else?

ANDWF f , d Logic AND between the content of W register with the content of a file register 'f'. 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'. Operation: (W).AND. (f) ® destination Description: AND the W register with register 'f'. If 'd' is 0 the result is stored in the W register. If 'd' is 1 the result is stored back in register 'f'.

I have read the data-sheet PIC18f2550 and the PIC18 Family Reference Manual and Looked All over the internet and Stackexchange. I simply have not found an understandable answer. If the "ANDWF & ANDLW" are truly "AND" Functions

ASSEMBLY LANGUAGE MPLAB PIC18f2550

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The IF, AND, THEN and END IF in your code are all statements affecting program flow, not mathematical operators.

The PIC18F2550 has an instruction CPFSEQ (compare w to f, skip next instruction if equal) which can be used to implement the AND function in your example, like this:-

_if:
  MOVLW  0
  CPFSEQ Variable_1  ; IF Variable_1 = 0  
  GOTO   _endif      
  MOVLW  1
  CPFSEQ Variable_2  ; AND variable_2 = 1 
  GOTO   _endif      
  .
  .                  ; THEN do what is needed       
  .
_endif:

Note: this code just shows the principle, and may not be the most efficient (eg. using TSTFSZ Variable_1 and BRA _endif would be faster and more compact).

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  • \$\begingroup\$ After Working with the CPFSEQ I found out my question was actually easier than the question I needed to ask! The real problem turned out to be an AND OR problem. \$\endgroup\$ – user66377 Apr 16 '15 at 22:06
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They're bit-wise AND instructions whereas if I'm reading your question correctly you're expecting a logical AND.

In these bit-wise AND instructions, each of the 8 bits of one operand are individually AND-ed with the appropriate bits of the other operand and the result is stored wherever specified.

So for example if your W register contains 0x23 and you execute a ANDLW 0x12 you will end up with 0x02 in W.

0x23   == 0b00100011  
0x12   == 0b00010010  
AND-ed == 0b00000010  
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  • \$\begingroup\$ So basically it is not a Logical AND.... \$\endgroup\$ – user66377 Apr 16 '15 at 19:18
  • \$\begingroup\$ Each individual bit gets a Logical AND, so if you feed those instructions appropriate operands you can make them look and act like logical ANDs... \$\endgroup\$ – brhans Apr 16 '15 at 19:20
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After Working with the CPFSEQ I found out my question was actually easier than the question I needed to ask!

The real problem turned out to be a combination AND OR problem.

If var_1 = 0 AND var_2 = 0 then GOTO Loop..... If var_1 > 0 OR var_2 > 1 then GOTO Continue.

May not be the most efficient but it does work.

Main:

MOVLW b'00000000'

 MOVWF    RxCount              ;Start Count at Zero

Loop:

MOVLW b'00000000' .....Set RxRegister to Zero Normally changes in

Program Routine.

MOVWF RxRegister

nop ....;Added because the next MOVWF had a

number > 0, didn't work right .

MOVLW b'00000000'

CPFSGT RxCount ....; if RxCount = Zero goto "If_Or_And" OR else GOTO Continue

GOTO If_Or_And

Continue

INCF       RxCount

CALL      Other_Routines      ;Get RxRegister Data

        GOTO     Loop 

If_Or_And:

TSTFSZ  RxRegister            ;if RxRegister > Zero then GOTO Continue: 

GOTO    Continue              ;if RxRegister = Zero then GOTO Loop: 

GOTO    Loop    
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