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Thread
'[PIC] Two's complement comparisons'
2008\10\28@001901
by
David Duffy (AVD)
I have an temperature controller application where I want to take action
based on the current temperature and low and high set points.
There's 3 registers in signed (two's complement) format:
curr_temp
lo_trip
hi_trip
The high and low set points are actually called from ee at the moment
but I can pre-fetch them into registers if that's easier.
I have code that works when using positive temps (0..127), but want to
change it to deal with -ve temperatures as well. (-127...+127)
2008\10\28@010345
by
cdb
::T he high and low set points are actually called from ee at the
:: moment
:: but I can pre-fetch them into registers if that's easier.
::
:: I have code that works when using positive temps (0..127), but
:: want to
:: change it to deal with -ve temperatures as well. (-127...+127)
Hi David,
I don't quite follow, are you looking for a conversion that takes your existing code and makes it signable, or asking about how to go about deducting one number from the other?
Wouldn't temporarily making the numbers positive work?
comf some_reg, f
incf some_reg,f
or if working via W reg sublw 0
I'm assuming your coding in assembler?
Colin
--
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2008\10\28@012358
by
David Duffy (AVD)
|
cdb wrote:
{Quote hidden}> ::T he high and low set points are actually called from ee at the
> :: moment
> :: but I can pre-fetch them into registers if that's easier.
> ::
> :: I have code that works when using positive temps (0..127), but
> :: want to
> :: change it to deal with -ve temperatures as well. (-127...+127)
>
> Hi David,
>
> I don't quite follow, are you looking for a conversion that takes your existing code and makes it signable, or asking about how to go about deducting one number from the other?
> Wouldn't temporarily making the numbers positive work?
>
> comf some_reg, f
> incf some_reg,f
>
> or if working via W reg sublw 0
>
> I'm assuming your coding in assembler?
>
Yes, coding in assembler.
I have one value that varies (temperature) along with low and high set
points. All are in signed (two's complement) format and are in
registers. (none are constants)
I need some code that can compare the current temperature with the two
set points and branch as below:
A) Current temperature is lower than low set point
B) Current temperature is between low and high set points
C) Current temperature is higher than high set point
I'm just having a mental block with this. It must be not that hard! :-)
David...
2008\10\28@013526
by
Marcel Birthelmer
> I need some code that can compare the current temperature with the two
> set points and branch as below:
> A) Current temperature is lower than low set point
> B) Current temperature is between low and high set points
> C) Current temperature is higher than high set point
>
>
David,
the easiest thing to do would be to subtract your value from the high set
point, check the result (look through the instruction set listing in the
data book to see how the flags are affected by the numbers), and then
subtract the low set point from your value.
- Marcel
2008\10\28@021612
by
Jinx
David,
movfw current
subwf high_trip,w
bnc hi_less ;branch if current > high
movfw current
xorwf high_trip,w
bz hi_less ;branch if current = high
movfw low_trip
subwf current,w
bnc low_gtr ;branch if current < low
movfw current
xorwf low_trip,w
bz low_gtr ;branch if current = low
hi_less nop
low_gtr nop
If you're using the 18F then you have the N and OV flags as well
as the CPF instructions
2008\10\28@022231
by
David Duffy (AVD)
Marcel Birthelmer wrote:
>> I need some code that can compare the current temperature with the two
>> set points and branch as below:
>> A) Current temperature is lower than low set point
>> B) Current temperature is between low and high set points
>> C) Current temperature is higher than high set point
>>
> David,
> the easiest thing to do would be to subtract your value from the high set
> point, check the result (look through the instruction set listing in the
> data book to see how the flags are affected by the numbers), and then
> subtract the low set point from your value.
> - Marcel
>
Aha, I need to check the result msb and not the carry bit!
I was too focussed on the carry bit but that's no use here.
David...
2008\10\28@033157
by
Tamas Rudnai
David,
Two's complement is good because you do not need extra for calculation or
comparison.
compare
movf first,W
subwf second,W
btfss STATUS,C
goto Greater ; W is greater than second
btfsc STATUS,Z
goto Equal ; they are equal
goto Less ; W is less than second
If you were looking for DC, then you would check if the low 4 bits (low
nibble) are greater or lower... therefore your range is -16..+15
Tamas
On Tue, Oct 28, 2008 at 6:22 AM, David Duffy (AVD) <
.....davidKILLspam@spam@audiovisualdevices.com.au> wrote:
{Quote hidden}> Marcel Birthelmer wrote:
> >> I need some code that can compare the current temperature with the two
> >> set points and branch as below:
> >> A) Current temperature is lower than low set point
> >> B) Current temperature is between low and high set points
> >> C) Current temperature is higher than high set point
> >>
> > David,
> > the easiest thing to do would be to subtract your value from the high set
> > point, check the result (look through the instruction set listing in the
> > data book to see how the flags are affected by the numbers), and then
> > subtract the low set point from your value.
> > - Marcel
> >
>
> Aha, I need to check the result msb and not the carry bit!
> I was too focussed on the carry bit but that's no use here.
> David...
> -
2008\10\28@080734
by
David Duffy
|
|
No, that's not the function I need. There's a changing value and *two*
set points. (one lower and one higher) Doing the subtracts and testing
the msb of the result works correctly.
David...
Tamas Rudnai wrote:
{Quote hidden}> David,
>
> Two's complement is good because you do not need extra for calculation or
> comparison.
>
> compare
> movf first,W
> subwf second,W
> btfss STATUS,C
> goto Greater ; W is greater than second
> btfsc STATUS,Z
> goto Equal ; they are equal
> goto Less ; W is less than second
>
>
> If you were looking for DC, then you would check if the low 4 bits (low
> nibble) are greater or lower... therefore your range is -16..+15
>
> Tamas
>
>
> On Tue, Oct 28, 2008 at 6:22 AM, David Duffy (AVD) <
>
davidKILLspamaudiovisualdevices.com.au> wrote:
>
>
>> Marcel Birthelmer wrote:
>>
>>>> I need some code that can compare the current temperature with the two
>>>> set points and branch as below:
>>>> A) Current temperature is lower than low set point
>>>> B) Current temperature is between low and high set points
>>>> C) Current temperature is higher than high set point
>>>>
>>>>
>>> David,
>>> the easiest thing to do would be to subtract your value from the high set
>>> point, check the result (look through the instruction set listing in the
>>> data book to see how the flags are affected by the numbers), and then
>>> subtract the low set point from your value.
>>> - Marcel
>>>
>>>
>> Aha, I need to check the result msb and not the carry bit!
>> I was too focussed on the carry bit but that's no use here.
>> David...
>> --
2008\10\28@085253
by
Harold Hallikainen
>> I need some code that can compare the current temperature with the two
>> set points and branch as below:
>> A) Current temperature is lower than low set point
>> B) Current temperature is between low and high set points
>> C) Current temperature is higher than high set point
>>
There's some window check code at
http://www.piclist.org/techref/microchip/rangechk.htm
Harold
--
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opportunities available!
2008\10\28@093110
by
Tamas Rudnai
Sorry, I do not get it, how do you make difference if +5 or -5 is less than
-128 ?
Or -120 or +120 is less than -128?
Tamas
On Tue, Oct 28, 2008 at 12:07 PM, David Duffy <
.....davidKILLspam.....audiovisualdevices.com.au> wrote:
{Quote hidden}> No, that's not the function I need. There's a changing value and *two*
> set points. (one lower and one higher) Doing the subtracts and testing
> the msb of the result works correctly.
> David...
>
> Tamas Rudnai wrote:
> > David,
> >
> > Two's complement is good because you do not need extra for calculation or
> > comparison.
> >
> > compare
> > movf first,W
> > subwf second,W
> > btfss STATUS,C
> > goto Greater ; W is greater than second
> > btfsc STATUS,Z
> > goto Equal ; they are equal
> > goto Less ; W is less than second
> >
> >
> > If you were looking for DC, then you would check if the low 4 bits (low
> > nibble) are greater or lower... therefore your range is -16..+15
> >
> > Tamas
> >
> >
> > On Tue, Oct 28, 2008 at 6:22 AM, David Duffy (AVD) <
> >
EraseMEdavidspam_OUTTakeThisOuTaudiovisualdevices.com.au> wrote:
> >
> >
> >> Marcel Birthelmer wrote:
> >>
> >>>> I need some code that can compare the current temperature with the two
> >>>> set points and branch as below:
> >>>> A) Current temperature is lower than low set point
> >>>> B) Current temperature is between low and high set points
> >>>> C) Current temperature is higher than high set point
> >>>>
> >>>>
> >>> David,
> >>> the easiest thing to do would be to subtract your value from the high
> set
> >>> point, check the result (look through the instruction set listing in
> the
> >>> data book to see how the flags are affected by the numbers), and then
> >>> subtract the low set point from your value.
> >>> - Marcel
> >>>
> >>>
> >> Aha, I need to check the result msb and not the carry bit!
> >> I was too focussed on the carry bit but that's no use here.
> >> David...
> >> --
2008\10\28@140307
by
Peter
David Duffy (AVD <david <at> audiovisualdevices.com.au> writes:
> I have code that works when using positive temps (0..127), but want to
> change it to deal with -ve temperatures as well. (-127...+127)
Just add the numbers together and check for carry and zero flags. You can figure
it out with a number axis drawing.
Peter
2008\10\28@171303
by
David Duffy
It's signed (two's complement) format. The MSB is the sign. (set when
negative)
David...
Tamas Rudnai wrote:
{Quote hidden}> Sorry, I do not get it, how do you make difference if +5 or -5 is less than
> -128 ?
> Or -120 or +120 is less than -128?
>
> Tamas
>
>
> On Tue, Oct 28, 2008 at 12:07 PM, David Duffy <
>
davidspam_OUTaudiovisualdevices.com.au> wrote:
>
>
>> No, that's not the function I need. There's a changing value and *two*
>> set points. (one lower and one higher) Doing the subtracts and testing
>> the msb of the result works correctly.
>> David...
>>
>> Tamas Rudnai wrote:
>>
>>> David,
>>>
>>> Two's complement is good because you do not need extra for calculation or
>>> comparison.
>>>
>>> compare
>>> movf first,W
>>> subwf second,W
>>> btfss STATUS,C
>>> goto Greater ; W is greater than second
>>> btfsc STATUS,Z
>>> goto Equal ; they are equal
>>> goto Less ; W is less than second
>>>
>>>
>>
2008\10\28@174619
by
Jinx
> > Sorry, I do not get it, how do you make difference if +5 or -5 is less
> > than -128 ?
> It's signed (two's complement) format. The MSB is the sign. (set when
> negative)
I think the point that Tamas was making is that there are two ways to
consider the values. Conceptually, the MSb being set denotes a negative
number. However, in reality, the byte contains only postive numbers
By setting the MSb, the most "negative" number becomes the most
"positive". It seems to me that you should complement the current value
before testing, as you've effectively inverted the scale between low
and high trigger points
2008\10\28@184354
by
Isaac Marino Bavaresco
|
You are forgetting the mathematical overflow.
Suppose you set the limits at +25 (lower) and +100 (upper ).
Value read: +10
+10 - ( +25 ) = -15
+10 - ( +100 ) = -90
So it is below both limits
Value read: +30
+30 - ( +25 ) = +5
+30 - ( +100 ) = -70
So it is between the lower and the upper limits.
Value read: +120
+120 - ( +25 ) = +95
+120 - ( +100 ) = +20
So it is above both limits.
But suppose you read -50
-50 - ( +25 ) = -75
-50 - ( +100 ) = -150 <= problem here. A 8-bit two's complement number
can not go below -128
-50 in two's complement is 206 and -100 is 156, so the above subtraction
becomes:
206 + 156 = 362. This number gets truncated to 106, which is positive.
That´s right: 206 + 156 = 106 !!!
You must test the OVERFLOW bit also, but the 12-bit and 14-bit
instruction PICs do not have it. The PIC18 has.
You will need to do more tests and calculations to get the correct result.
David Duffy escreveu:
{Quote hidden}> It's signed (two's complement) format. The MSB is the sign. (set when
> negative)
> David...
>
> Tamas Rudnai wrote:
>
>> Sorry, I do not get it, how do you make difference if +5 or -5 is less than
>> -128 ?
>> Or -120 or +120 is less than -128?
>>
>> Tamas
>>
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2008\10\28@190904
by
Harold Hallikainen
|
>> > Sorry, I do not get it, how do you make difference if +5 or -5 is less
>> > than -128 ?
>
>> It's signed (two's complement) format. The MSB is the sign. (set when
>> negative)
>
> I think the point that Tamas was making is that there are two ways to
> consider the values. Conceptually, the MSb being set denotes a negative
> number. However, in reality, the byte contains only postive numbers
>
> By setting the MSb, the most "negative" number becomes the most
> "positive". It seems to me that you should complement the current value
> before testing, as you've effectively inverted the scale between low
> and high trigger points
>
Another way of thinking of two's complement numbers is to consider, just
like unsigned binary, each bit has a "weight." For 8 bit unsigned, the
weight of the msb is +128. For two's complement, the weight of the msb is
-128. Otherwise, the interpretation of the number is the same (add the
weights where the corresponding bit is a 1).
For the task at hand, doing a window comparison on two's complement
numbers, you could use the unsigned code I posted before, but add 128 to
each number before passing it in to the comparison routine. This biases
the signed numbers up to always be between 0 and 255.
Harold
--
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opportunities available!
2008\10\28@203557
by
David Duffy (AVD)
Harold Hallikainen wrote:
> For the task at hand, doing a window comparison on two's complement
> numbers, you could use the unsigned code I posted before, but add 128 to
> each number before passing it in to the comparison routine. This biases
> the signed numbers up to always be between 0 and 255.
>
Yes, I thought of doing the same thing (biasing it up by 128) but ended
up with testing the msb which seems to work for all test cases I've tried.
David...
2008\10\28@212706
by
David Duffy (AVD)
|
|
OK, so it looks as though my method only works for a range values. Not
good. I will instead just add 128 to all numbers first (to pull them
into a 0-255 range) and then do the comparisons. Thanks everyone for
their input.
David...
Isaac Marino Bavaresco wrote:
{Quote hidden}> You are forgetting the mathematical overflow.
>
> Suppose you set the limits at +25 (lower) and +100 (upper ).
>
> Value read: +10
>
> +10 - ( +25 ) = -15
> +10 - ( +100 ) = -90
> So it is below both limits
>
> Value read: +30
>
> +30 - ( +25 ) = +5
> +30 - ( +100 ) = -70
> So it is between the lower and the upper limits.
>
> Value read: +120
>
> +120 - ( +25 ) = +95
> +120 - ( +100 ) = +20
> So it is above both limits.
>
> But suppose you read -50
>
> -50 - ( +25 ) = -75
> -50 - ( +100 ) = -150 <= problem here. A 8-bit two's complement number
> can not go below -128
>
> -50 in two's complement is 206 and -100 is 156, so the above subtraction
> becomes:
>
> 206 + 156 = 362. This number gets truncated to 106, which is positive.
> That´s right: 206 + 156 = 106 !!!
>
> You must test the OVERFLOW bit also, but the 12-bit and 14-bit
> instruction PICs do not have it. The PIC18 has.
>
> You will need to do more tests and calculations to get the correct result.
>
> David Duffy escreveu:
>
>> It's signed (two's complement) format. The MSB is the sign. (set when
>> negative)
>> David...
>>
>> Tamas Rudnai wrote:
>>
>>
>>> Sorry, I do not get it, how do you make difference if +5 or -5 is less than
>>> -128 ?
>>> Or -120 or +120 is less than -128?
>>>
>>> Tamas
>>>
>>>
> __________________________________________________
> Faça ligações para outros computadores com o novo Yahoo! Messenger
>
http://br.beta.messenger.yahoo.com/
>
>
--
___________________________________________
David Duffy Audio Visual Devices P/L
Unit 8, 10 Hook St, Capalaba 4157 Australia
Ph: +61 7 38235717 Fax: +61 7 38234717
Our Web Site: http://www.audiovisualdevices.com.au
___________________________________________
2008\10\29@020848
by
Wouter van Ooijen
> I think the point that Tamas was making is that there are two ways to
> consider the values. Conceptually, the MSb being set denotes a negative
> number. However, in reality, the byte contains only postive numbers
There is no reality, only interpretation. Two of the possible
interpretations are "binary unsigned" and "binary 2-s complement". "2-s
complement" can indeed be visualized the way you describe.
--
Wouter van Ooijen
-- -------------------------------------------
Van Ooijen Technische Informatica: http://www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: http://www.voti.nl/hvu
2008\10\29@034714
by
Jinx
> the byte contains only postive numbers
>
> There is no reality, only interpretation
That's correct, and I did think about "representation" after the
mail had gone
2008\10\29@213704
by
Isaac Marino Bavaresco
|
|
David Duffy (AVD) escreveu:
> OK, so it looks as though my method only works for a range values. Not
> good. I will instead just add 128 to all numbers first (to pull them
> into a 0-255 range) and then do the comparisons. Thanks everyone for
> their input.
> David...]
I just wrote some C code and looked at the compiler generated assembly
code. After some hand-optimizations I got the following (be careful, I
may have introduced some errors):
;==============================================================
; signed char Var_a, Var_b, Tmp;
;==============================================================
; if( Var_a < Var_b )
A_LESS_THAN_B:
movf Var_a,W
xorlw 0x80
movwf Tmp
movf Var_b,W
xorlw 0x80
subwf Tmp,F
btfsc STATUS,C
goto A_LESS_THAN_B_FALSE
A_LESS_THAN_B_TRUE:
; Your code here
A_LESS_THAN_B_FALSE:
;==============================================================
; if( Var_a <= Var_b )
A_LESS_THAN_OR_EQUAL_TO_B:
movf Var_b,W
xorlw 0x80
movwf Tmp
movf Var_a,W
xorlw 0x80
subwf Tmp,F
btfss STATUS,C
goto A_LESS_THAN_OR_EQUAL_TO_B_FALSE
A_LESS_THAN_OR_EQUAL_TO_B_TRUE:
; Your code here
A_LESS_THAN_OR_EQUAL_TO_B_FALSE:
;==============================================================
; if( Var_a == Var_b )
A_EQUAL_TO_B:
movf Var_a,W
xorwf Var_b,W
btfss STATUS,Z
goto A_EQUAL_TO_B_FALSE
A_EQUAL_TO_B_TRUE:
; Your code here
A_EQUAL_TO_B_FALSE:
;==============================================================
; if( Var_a >= Var_b )
A_GREATER_THAN_OR_EQUAL_TO_B:
movf Var_a,W
xorlw 0x80
movwf Tmp_a
movf Var_b,W
xorlw 0x80
subwf Tmp_a,F
btfss STATUS,C
goto A_GREATER_THAN_OR_EQUAL_TO_B_FALSE
A_GREATER_THAN_OR_EQUAL_TO_B_TRUE:
; Your code here
A_GREATER_THAN_OR_EQUAL_TO_B_FALSE:
;==============================================================
; if( Var_a > Var_b )
A_GREATER_THAN_B:
72 047 0871 movf Var_b,W
73 048 3A80 xorlw 0x80
74 049 00F3 movwf Tmp
70 045 0870 movf Var_a,W
76 04B 3A80 xorlw 0x80
77 04C 02F3 subwf Tmp,F
78 04D 1803 btfsc STATUS,C
79 04E 2850 goto A_GREATER_THAN_B_FALSE
A_GREATER_THAN_B_TRUE:
; Your code here
A_GREATER_THAN_B_FALSE:
;==============================================================
PS.: You may convert the above code into macros to make it easier to use
them.
PPS.: Some time ago somebody talked about Hi-Tech PICC-Lite versus PRO
generated code.
I found that the Lite generates purposely (very) inefficient code, so
the PRO version looks even better.
Look how they do 'Var = 0;' :
bcf STATUS,C
movlw 0
btfsc STATUS,C
movlw 1
movwf Var
'Var = 1;'
clrf Var
bsf STATUS,C
rlf Var,f
'Var = 2;'
clrw
iorlw 2
movwf Temp
movf Temp,w
movwf Var
And so on...
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2008\10\29@223453
by
cdb
2008\10\30@054326
by
Tamas Rudnai
In my opinion you just have to rotate both numbers by 1 to the left, so the
range -128 .. +127 becomes 0..255 and the comparison can be made by simple
subwf or sublw and then you can check the C.
Something like:
storeLimit macro limit ; desired limit in W
addlw .128 ; this is the rotation by 1...
movwf limit
endm
start
movlw .100
storeLimit high_limit
movlw -.50
storeLimit low_limit
test_value
movlw .50
compare ; current value in W
;----- if W is less or equal than the high_limit
addlw .128
subwf high_limit, W
btfss STATUS,C
goto out_of_range
;----- if W is greater or equal than low_limit
; restoring W for further checkings
subwf high_limit, W
; now we can check for low
subwf low_limit, W
btfss STATUS,Z ; are they equal?
btfss STATUS,C
goto in_range
goto out_of_range
We needed two extra instruction for the low_limit checkings (restoring W and
check if W is equal to the limit), however, if that is essential we can
store the low limit as the difference from the high limit so the W
restoration is not needed plus we can reduce that number by 1 so there is no
need to check for equality...
Tamas
On Thu, Oct 30, 2008 at 1:39 AM, Isaac Marino Bavaresco <
KILLspamisaacbavarescoKILLspamyahoo.com.br> wrote:
{Quote hidden}> David Duffy (AVD) escreveu:
> > OK, so it looks as though my method only works for a range values. Not
> > good. I will instead just add 128 to all numbers first (to pull them
> > into a 0-255 range) and then do the comparisons. Thanks everyone for
> > their input.
> > David...]
> I just wrote some C code and looked at the compiler generated assembly
> code. After some hand-optimizations I got the following (be careful, I
> may have introduced some errors):
>
> ;==============================================================
>
> ; signed char Var_a, Var_b, Tmp;
>
> ;==============================================================
> ; if( Var_a < Var_b )
>
> A_LESS_THAN_B:
> movf Var_a,W
> xorlw 0x80
> movwf Tmp
> movf Var_b,W
> xorlw 0x80
> subwf Tmp,F
> btfsc STATUS,C
> goto A_LESS_THAN_B_FALSE
>
> A_LESS_THAN_B_TRUE:
>
> ; Your code here
>
> A_LESS_THAN_B_FALSE:
>
> ;==============================================================
> ; if( Var_a <= Var_b )
>
> A_LESS_THAN_OR_EQUAL_TO_B:
>
> movf Var_b,W
> xorlw 0x80
> movwf Tmp
>
> movf Var_a,W
> xorlw 0x80
>
> subwf Tmp,F
> btfss STATUS,C
> goto A_LESS_THAN_OR_EQUAL_TO_B_FALSE
>
> A_LESS_THAN_OR_EQUAL_TO_B_TRUE:
>
> ; Your code here
>
> A_LESS_THAN_OR_EQUAL_TO_B_FALSE:
>
> ;==============================================================
> ; if( Var_a == Var_b )
>
> A_EQUAL_TO_B:
>
> movf Var_a,W
> xorwf Var_b,W
> btfss STATUS,Z
> goto A_EQUAL_TO_B_FALSE
>
> A_EQUAL_TO_B_TRUE:
>
> ; Your code here
>
> A_EQUAL_TO_B_FALSE:
>
> ;==============================================================
> ; if( Var_a >= Var_b )
>
> A_GREATER_THAN_OR_EQUAL_TO_B:
>
> movf Var_a,W
> xorlw 0x80
> movwf Tmp_a
>
> movf Var_b,W
> xorlw 0x80
>
> subwf Tmp_a,F
> btfss STATUS,C
> goto A_GREATER_THAN_OR_EQUAL_TO_B_FALSE
>
> A_GREATER_THAN_OR_EQUAL_TO_B_TRUE:
>
> ; Your code here
>
> A_GREATER_THAN_OR_EQUAL_TO_B_FALSE:
>
> ;==============================================================
> ; if( Var_a > Var_b )
>
> A_GREATER_THAN_B:
>
> 72 047 0871 movf Var_b,W
> 73 048 3A80 xorlw 0x80
> 74 049 00F3 movwf Tmp
>
> 70 045 0870 movf Var_a,W
> 76 04B 3A80 xorlw 0x80
>
> 77 04C 02F3 subwf Tmp,F
> 78 04D 1803 btfsc STATUS,C
> 79 04E 2850 goto A_GREATER_THAN_B_FALSE
>
> A_GREATER_THAN_B_TRUE:
>
> ; Your code here
>
> A_GREATER_THAN_B_FALSE:
>
> ;==============================================================
>
> PS.: You may convert the above code into macros to make it easier to use
> them.
>
> PPS.: Some time ago somebody talked about Hi-Tech PICC-Lite versus PRO
> generated code.
> I found that the Lite generates purposely (very) inefficient code, so
> the PRO version looks even better.
>
> Look how they do 'Var = 0;' :
>
> bcf STATUS,C
> movlw 0
> btfsc STATUS,C
> movlw 1
> movwf Var
>
> 'Var = 1;'
>
> clrf Var
> bsf STATUS,C
> rlf Var,f
>
> 'Var = 2;'
>
> clrw
> iorlw 2
> movwf Temp
> movf Temp,w
> movwf Var
>
> And so on...
> __________________________________________________
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>
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>
>
2008\10\30@065104
by
cdb
2008\10\30@075852
by
Isaac Marino Bavaresco
I didn't get your point,
You are saying that Hi-Tech didn't crippled PICC Lite on purpose or that
the code example I presented don't work?
cdb escreveu:
{Quote hidden}
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2008\10\30@081340
by
cdb
:: I didn't get your point,
::
:: You are saying that Hi-Tech didn't crippled PICC Lite on purpose
:: or that
:: the code example I presented don't work?
No, what I meant was the order in which you gave the code was the
wrong way around.
You posted.
Look how they do 'Var = 0;' :
bcf STATUS,C
movlw 0
btfsc STATUS,C
movlw 1
movwf Var // I think you intended Var = 1
'Var = 1;'
clrf Var
bsf STATUS,C
rlf Var,f // Var = 0
Or am I all at 6's and 7's ? :)
Colin
--
cdb, TakeThisOuTcolinEraseMEspam_OUTbtech-online.co.uk on 30/10/2008
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2008\10\30@082714
by
Isaac Marino Bavaresco
cdb escreveu:
> :: so the range -128 .. +127 becomes 0..255
>
> You'd need to have a clear carry instruction, after each of the calls
> to storeLimit, otherwise if you had a value of -128 the Carry flag
> would be set on exit of the macro.
>
> Making the subsequent test of the Carry flag liable to error.
>
> Colin
> --
> cdb, RemoveMEcolinTakeThisOuTbtech-online.co.uk on 30/10/2008
>
> Web presence: http://www.btech-online.co.uk
>
> Hosted by: http://www.1and1.co.uk/?k_id=7988359
>
If the Carry Flag is the problem, you may use 'xorlw .128' instead of
'addlw .128'.
Both have the same effect on WREG (toggling the high order bit), but the
first don't change the Carry Flag.
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2008\10\30@083122
by
Isaac Marino Bavaresco
Tamas Rudnai escreveu:
> In my opinion you just have to rotate both numbers by 1 to the left, so the
> range -128 .. +127 becomes 0..255 and the comparison can be made by simple
> subwf or sublw and then you can check the C.
>
> Something like:
>
> storeLimit macro limit ; desired limit in W
> addlw .128 ; this is the rotation by 1...
> movwf limit
> endm
>
OK, 'addlw .128' will offset the value range up so you can do an
unsigned test, but I would hardly call it "rotate 1 to the left".
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2008\10\30@085029
by
Isaac Marino Bavaresco
|
|
cdb escreveu:
> :: I didn't get your point,
> ::
> :: You are saying that Hi-Tech didn't crippled PICC Lite on purpose
> :: or that
> :: the code example I presented don't work?
>
> No, what I meant was the order in which you gave the code was the
> wrong way around.
>
> You posted.
>
> Look how they do 'Var = 0;' :
>
> bcf STATUS,C
> movlw 0
> btfsc STATUS,C
> movlw 1
> movwf Var // I think you intended Var = 1
>
bcf STATUS,C CARRY = 0
movlw 0 WREG = 0
btfsc STATUS,C Skip next instruction if CARRY is clear ( == 0 )
movlw 1 This instruction is never executed
movwf Var Var = WREG
Usually just a 'clrf Var' is enough.
> 'Var = 1;'
>
> clrf Var
> bsf STATUS,C
> rlf Var,f // Var = 0
>
clrf Var Var = 0
bsf STATUS,C CARYY = 1
rlf Var,f Rotate Var to left, inserting CARRY flag into bit 0
One way to do this is:
clrf Var
incf Var,f
Best regards,
Isaac
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2008\10\30@091429
by
cdb
2008\10\30@101010
by
Tamas Rudnai
> OK, 'addlw .128' will offset the value range up so you can do an
> unsigned test, but I would hardly call it "rotate 1 to the left".
You are right, I was so much concentrating on overflowing the negative
numbers, but yes, this is not a rotation of course, and has the same effect
as with the xorlw 0x80.
Cheers,
Tamas
On Thu, Oct 30, 2008 at 12:24 PM, Isaac Marino Bavaresco <
EraseMEisaacbavarescoyahoo.com.br> wrote:
{Quote hidden}> Tamas Rudnai escreveu:
> > In my opinion you just have to rotate both numbers by 1 to the left, so
> the
> > range -128 .. +127 becomes 0..255 and the comparison can be made by
> simple
> > subwf or sublw and then you can check the C.
> >
> > Something like:
> >
> > storeLimit macro limit ; desired limit in W
> > addlw .128 ; this is the rotation by 1...
> > movwf limit
> > endm
> >
>
> OK, 'addlw .128' will offset the value range up so you can do an
> unsigned test, but I would hardly call it "rotate 1 to the left".
>
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