Wierd result when inverting an input


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  1. #1
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    Default Wierd result when inverting an input

    Bell var portB.0
    Report var byte

    (PortB.0 is pulled up)

    Report = !Bell + 48 or Report = (!Bell) + 48

    The value of variable Report = "0" (ascii 48) when portB.0 = True
    The value of variable Report = "/" (ascii 47) when portB.0 = False (I was expecting ascii 49)

    Is this a bug in PBP3 or I am using wrongly the not notation?

    Cheers

    Al
    All progress began with an idea

  2. #2
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    Default Re: Wierd result when inverting an input

    Al, I believe you have to use the BITWISE operator of "~" for that operation.
    Dave Purola,
    N8NTA
    EN82fn

  3. #3
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    Default Re: Wierd result when inverting an input

    Thank you Dave for the suggestion, but no luck it doesn't work either. With "~" I get ascii 46 when portB.0 is false and the same ascii 47 when the portB.0 is True.

    Looking into the manual the character for the NOT is "!", I could not find any reference to "~" as a NOT notation.

    Cheers

    Al.
    All progress began with an idea

  4. #4
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    Default Re: Wierd result when inverting an input

    Quote Originally Posted by aratti View Post
    Thank you Dave for the suggestion, but no luck it doesn't work either. With "~" I get ascii 46 when portB.0 is false and the same ascii 47 when the portB.0 is True.

    Looking into the manual the character for the NOT is "!", I could not find any reference to "~" as a NOT notation.

    Cheers

    Al.
    The "tilde" character ~ is a BITWISE NOT. pp35 in the old green book, have misplaced my PBP3 book.

    This works:
    Code:
    Bell var portB.6
    Report var byte
    main:
    Report = ~~(Bell + 48) 
    debug report
    pause 500
    
    goto main
    Last edited by Archangel; - 19th June 2015 at 18:02.
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  5. #5
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    Default Re: Wierd result when inverting an input

    Code:
    Bell var portB.6
    Report var byte
    main:
    Report = ~~(Bell + 48) 
    debug report
    pause 500
    
    goto main
    Thank you Archangel for your snippet.
    I tried with one tilde character ~(Bell + 48) and it does't work. (Just strange characters)
    I tried with two tildes, as per your example, and what I get is the original Logic state of the pin. It seems that two tildes are simply ignored.

    So, at the moment I have used the IF/THEN/ELSE/ENDIF workaround. Conclusion we cannot invert a pin alias and convert it to ascii using the "!" or the bitwise "~"

    Cheers
    Al.
    Last edited by aratti; - 19th June 2015 at 18:57.
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  6. #6
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    Default Re: Wierd result when inverting an input

    It seems that two tildes are simply ignored.
    not at all !

    PORTB = ~ PORTB ' Invert every bit in PORTB
    result = ~ (PORTB & %00001111)
    'Invert the result of the & operation
    manual $ 3.2.4 ...

    if you invert twice ... you get the original value !!!

    did you try ...
    Code:
    Report = (~ Bell ) + 48 ...
    probably not !
    Alain
    Last edited by Acetronics2; - 19th June 2015 at 19:51.
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    IF there is the word "Problem" in your question ...
    certainly the answer is " RTFM " or " RTFDataSheet " !!!
    *****************************************

  7. #7
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    Default Re: Wierd result when inverting an input

    Alain, the result of your example : Report = (~ Bell ) + 48 gives 46 when input is high and 47 when the input is low.

    Cheers

    Al.
    All progress began with an idea

  8. #8
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    Default Re: Wierd result when inverting an input

    Al, It makes me wonder if the TRIS register is set correctly for the port? You always get the same response no mater what state you place on it.
    Dave Purola,
    N8NTA
    EN82fn

  9. #9
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    Default Re: Wierd result when inverting an input

    Just thinking here....

    What you might be seeing is that in a single statement "Report = (~Bell) + 48", is that PBP is treating the combination of the alias and the assignment to "Report" as a byte output computation.

    If that is the case, then the output is as expected.
    Byte variables are unsigned, so a bitwise not of 0 = 255 and 1 = 254.
    Which would give you the 47 and 46 values you are seeing. 255+48=47, 254+48=46

    This is most likely also happening for the Logical Not as well.

    To test:

    Bell var PORTB.6
    Report var byte
    MyPin var bit

    MyPin = Bell
    MyPin = ~MyPin 'this will force the bitwise Not at the bit variable level
    Report = MyPin + 48

    MyPin = Bell
    MyPin = !Mypin 'This will force the logical Not at the bit variable level
    Report = MyPin + 48

    Output the two operations and see what you get then.
    Regards,
    TABSoft

  10. #10
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    Default Re: Wierd result when inverting an input

    Hi, Al

    I played somewhat with that and end with ...

    Code:
    Report = 47 - (~Bell)
    found funny things like ~N = 65535 - N ...

    Have a good night
    Alain
    ************************************************** ***********************
    Why insist on using 32 Bits when you're not even able to deal with the first 8 ones ??? ehhhhhh ...
    ************************************************** ***********************
    IF there is the word "Problem" in your question ...
    certainly the answer is " RTFM " or " RTFDataSheet " !!!
    *****************************************

  11. #11
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    Default Re: Wierd result when inverting an input

    Dave, the tris register is set correctly and the pic18f2620 just do what it should do when the inputs change Logic state. I need to invert the Logic state of the display (it is much more simple to have a "True" when the external sensor is close instead having a "False".
    As I said in a previous post, I solved the problem using the following workaround:
    Code:
    If Bell = false then
    Report = "1"
    Else
    Report = "0"
    ENDIF
    Definetly less elegant than the "NOT" notation but at least it works!

    Since I always toggle the flashing led with led = !led and it works fine I wrongly assumed that it could work also with an alias. Very likely I should copy the pin state in a bit variable to have it working. I will give a tray (NOT NOW)

    Cheers
    Al.
    All progress began with an idea

  12. #12
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    Default Re: Wierd result when inverting an input

    Code:
    MyPin = Bell
    MyPin = !Mypin 'This will force the logical Not at the bit variable level
    Report = MyPin + 48
    Thank you Tabsoft for the above snippet. Tested and it works. I have already replaced the IF/THEN/ELSE code that I could not stand with.

    Now that a more elegant workaround has been found, the question remains: PBP3 cannot handle pin alias. Is it a bug?

    Cheers

    Al
    All progress began with an idea

  13. #13
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    Default Re: Wierd result when inverting an input

    Glad it worked.

    I have a theory, but will want to test it and look at the disassembled code to see.

    I think it is the fact that the NOT operator (logical or bitwise) against the alias is being evaluated in an assignment statement to a byte.
    This may be having the compiler use a generic macro that is handling the NOT operation as a byte or word output.
    The test code above should force a two-step process.
    1. Force the NOT operation/assignment to a bit variable.
    2. Assign the value + 48 to the Report byte variable.

    My guess is that since "Report = !Bell + 48" has the Report byte variable on the left, PBP might be assuming that the interim steps are at a byte (or word) level.

    We will see, or I could be totally wrong. :-0

    Either way I don't think we should have to burn another variable and cycles to perform what should be a simple function.
    Regards,
    TABSoft

  14. #14
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    Default Re: Wierd result when inverting an input

    Well, it was as I expected.

    It's all about the assignment statement.

    Whatever "Type" the left side of the assignment statement is drives the operation.
    If you are assigning the value to a Byte, then the compiler does the steps as a byte.
    If you are assigning the value to a BIT, then the compiler does the steps as a bit.

    Here is a simple test program.
    The "Destination" of the value is tested against a Byte variable or a Bit variable.
    The "Source" of the value is tested against a Byte variable, a Port Alias and a Bit Alias.


    Code:
    myBit var bit
    myByte var byte
    
    TRISB = $FF
    
    TestPin var PORTB.6
    TestByte var byte
    TestBit var TestByte.6
    
    
    'Test Variable Alias with direct assignment to byte variable
    TestByte = %01000000
    
    'Assign Logical NOT (!) bit value to byte variable
    myByte = !TestBit
    
    'Assign Bitwise NOT (~) bit value to byte variable
    myByte = ~TestBit
    
    'Test Port Alias with direct assignment to byte variable
    
    'Assign Logical NOT (!) bit value to byte variable
    myByte = !TestPin
    
    'Assign Bitwise NOT (~) bit value to byte variable
    myByte = ~TestPin
    
    'Test Variable Alias with direct assignment to bit variable
    TestByte = %01000000
    
    'Assign Logical NOT (!) bit value to bit variable
    myBit = !TestBit
    
    'Assign Bitwise NOT (~) bit value to bit variable
    myBit = ~TestBit
    
    'Test Port Alias with direct assignment to bit variable
    
    'Assign Logical NOT (!) bit value to byte variable
    myBit = !TestPin
    
    'Assign Bitwise NOT (~) bit value to byte variable
    myBit = ~TestPin

    Here is the PBP assembler listing for the above code.
    Notice that there are (2) macros for each operator type (! or ~)
    LNOT?TB and LNOT?TT (Logical NOT !)
    NOT?TB and NOT?TT (Bitwise NOT ~)

    The TB stands for biT in and Byte out. The input is a Bit type and the Output is a Byte type.
    This is when you get the results that are not what you might expect.

    The TT stands for biT in and biT out. The input is a Bit type and the Output is a Bit type.


    Code:
    ;assembler variables
    _myByte          		EQU	RAM_START + 01Ah
    PB01            		EQU	RAM_START + 01Bh
    _TestByte        		EQU	RAM_START + 01Ch
    
    ;assembler defines
    #define _myBit           	 PB01, 000h
    #define _TestPin         	_PORTB??6
    #define _TestBit         	_TestByte??6
    #define _PORTB??6        	 PORTB, 006h
    #define _TestByte??6     	_TestByte, 006h
    
    
    ; 00022	TestByte = %01000000
    	MOVE?CB	040h, _TestByte
    
    ; 00025	myByte = !TestBit
    	LNOT?TB	_TestBit, _myByte
    
    ; 00028	myByte = ~TestBit
    	NOT?TB	_TestBit, _myByte
    
    ; 00033	myByte = !TestPin
    	LNOT?TB	_TestPin, _myByte
    
    ; 00036	myByte = ~TestPin
    	NOT?TB	_TestPin, _myByte
    
    ; 00039	TestByte = %01000000
    	MOVE?CB	040h, _TestByte
    
    ; 00042	myBit = !TestBit
    	LNOT?TT	_TestBit, _myBit
    
    ; 00045	myBit = ~TestBit
    	NOT?TT	_TestBit, _myBit
    
    ; 00050	myBit = !TestPin
    	LNOT?TT	_TestPin, _myBit
    
    ; 00053	myBit = ~TestPin
    	NOT?TT	_TestPin, _myBit
    Here are the actual macros that are called above.
    I made some comments, not for everything but some.

    Code:
    NOT?TB macro Regin, Bitin, Bout
            CHK?RP  Regin
            movlw   -1  ;load dec 255 into w register
            btfsc   Regin, Bitin    ;If Regin.Bitin = 0, skip the next instruction
            movlw   -2  ;load dec 254 into w register
            MOVE?AB Bout    ;Move W to Bout
        endm
    
    NOT?TT macro Regin, Bitin, Regout, Bitout
            CHK?RP  Regin
            clrw    ;Clear the w register
            btfss   Regin, Bitin    ;If Regin.Bitin = 1, skip the next instruction
            addlw   1   ;Load dec 1 into the w Register
            CHK?RP  Regout
            btfsc   STATUS, Z
            bcf     Regout, Bitout  ;Clear Regout.Bitout
            btfss   STATUS, Z
            bsf     Regout, Bitout  ;Set Regout.Bitout
        endm
    
    LNOT?TB macro Regin, Bitin, Bout
            CHK?RP  Regin
            clrw
            btfss   Regin, Bitin
            movlw   -1
            MOVE?AB Bout
        endm
    
    LNOT?TT macro Regin, Bitin, Regout, Bitout
            CHK?RP  Regin
            clrw
            btfss   Regin, Bitin
            addlw   1
            CHK?RP  Regout
            btfsc   STATUS, Z
            bcf     Regout, Bitout
            btfss   STATUS, Z
            bsf     Regout, Bitout
        endm
    Regards,
    TABSoft

  15. #15
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    Default Re: Wierd result when inverting an input

    Thank you Tabsoft for the deep search!

    I think that this finding should call for an update of the manual (at least)

    Cheers

    Al.
    All progress began with an idea

  16. #16
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    Default Re: Wierd result when inverting an input

    BTW,

    I remember Darrel had written a post about this kind of behaviour.
    he used a "!!" to get rid of the problem.

    does somebody remember where it was shown ???

    Alain
    ************************************************** ***********************
    Why insist on using 32 Bits when you're not even able to deal with the first 8 ones ??? ehhhhhh ...
    ************************************************** ***********************
    IF there is the word "Problem" in your question ...
    certainly the answer is " RTFM " or " RTFDataSheet " !!!
    *****************************************

  17. #17
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    Default Re: Wierd result when inverting an input

    That post would be interesting to read.
    I don't see how it would alleviate the issue.
    I think without an interim step to force the assignment to a bit type variable it will perform the operation as a byte.

    I might take a look through the PBP library macros for Logical and bitwise NOTs to see if there is another macro that would hand the situation. If there is, it would be a matter of what syntax would cause the compiler to pick that macro instead.
    Regards,
    TABSoft

  18. #18
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    Default Re: Wierd result when inverting an input

    It would seem that the simple way around this is:

    Report = 48 + !Mypin

    Wouln't that force
    Picbasic to evaluate Report as a byte, not as a bit?

  19. #19
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    Default Re: Wierd result when inverting an input

    No, not really.
    That has been the point of this discussion.

    We would not want PBP to do the interim calculations as a byte, we would want PBP to do them as a bit.

    The issue is that in this statement "Report = 48 + !Mypin"
    Report is a byte variable, 48 will be treated as a constant and Mypin is a bit.
    Sounds good so far, but, when PBP looks at this statement it will treat the !Mypin as a byte output in the calculation step.
    It does this because "Report" on the left side is a byte variable.

    What we want is if Mypin = 0 then Report = 49; If Mypin = 1 then Report = 48.

    But here is what happens.

    Pseudocode for the PBP ASM Macros used for the following Statement: Report = 48 + !Mypin
    Code:
    Step 1. Perform a Logical NOT on Mypin.
        Clear the W register (Set it to 0)
        If Mypin is a zero then 
            Store 255 decimal in the W register  'This is because Report will ultimately get the value, so PBP starts treating all the output variables as bytes
        else
            Store 0 in W register
        endif
        Move W register to a temporary "byte" variable T1
        
    Step 2. Add 48 to temporary "byte" variable T1
            
    Step 3. Move Temporary "byte" variable T1 to "byte" variable Report
    So if you start with Mypin = 0, then
    Code:
    Step 1. T1 = 255
    Step 2. T1 = 255 + 48 = 47   ' This is because a byte variable is unsigned in PBP
    Step 3. Report = 47 'We wanted Report to equal 49 not 47
    
    If you start with Mypin = 1
    Step 1. T1 = 0
    Step 2. T1 = 0 + 48 = 48
    Step 3. Report = 48 'This is what we wanted.
    So the issue as I can see is that to perform this logic as we "want" it to work, you need to manually perform an interim step
    and store the current value of Mypin in a "bit" variable. Then perform a logical NOT on the "bit" variable. Then add 48 and the "bit" variable
    and store the answer in report.

    myBit var bit
    Mypin var PORTB.6
    Report var byte

    myBit = Mypin
    myBit = !myBit
    Report = 48 + myBit

    This works.
    Regards,
    TABSoft

  20. #20
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    Default Re: Wierd result when inverting an input

    And the answer is....
    Mypin var Portb.6
    Report var byte

    Report = 48 + (Mypin ^ 1)

    There is NO need to be changing variable types. Mypin just needs to be inverted. So why not invert it as if it is a bit. Wow all of this typing for something so simple......
    Dave Purola,
    N8NTA
    EN82fn

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