Hi,

You are forgetting that after the rotate the lsb is left in the carry
and what was in the carry is now in the msb.  You can get fancy and
first set the carry to the value of pwm.0 or try the following for fun.

        char LpDec @ pDecArg;
        char HpDec @ pDecArg+1;

        bHB_LED = pDecArg & 1;
        HpDec = LpDec;
        pDecArg >>= 1;

Now although this C code looks overly complex,  look at the code it
makes.  Ignore for the moment that Bytecraft C 1.4 sets the RPx bits for
any jump destination.  The first statement is the same as the bit
operations as if it were a ch.0 test.

One difference with this code is that the value is only tested once.  If
the location were a port pin that was changing from an outside source
the CC5x compiler generates code that might never light the LED since
the first test fails and then the second test fails because the input
value changed.  Very dangerous in real time systems.

Once the LED value is set the shift is kind of neat.  Copy the Least Sig
byte of the word into the upper byte.  Then shift it right one bit.  The
RRF 3F moves the lsb of the 8 bit variable into the carry.  The RRF 3E
then moves that bit into bit 7 and loses the lsb into the carry.

It may look like a waste of memory to use two bytes but you can see the
compiler here just stuffs the character we want to rotate into a
variable used for all sorts of I/O.


08C5 1283    BCF    STATUS,RP0        bHB_LED = pDecArg & 1;
08C6 1303    BCF    STATUS,RP1
08C7 183E    BTFSC  3E,0
08C8 28CB    GOTO   08CBh
08C9 1205    BCF    PORTA,4
08CA 28CE    GOTO   08CEh
08CB 1283    BCF    STATUS,RP0
08CC 1303    BCF    STATUS,RP1
08CD 1605    BSF    PORTA,4
08CE 1283    BCF    STATUS,RP0        HpDec = LpDec;
08CF 1303    BCF    STATUS,RP1
08D0 083E    MOVF   3E,W
08D1 00BF    MOVWF  3F
08D2 1003    BCF    STATUS,C          pDecArg >>= 1;
08D3 0CBF    RRF    3F
08D4 0CBE    RRF    3E


You might want to enter and leave this function with a
        LpDec = pwm;
        ...
        pwm = LpDec;

Or be real sneaky and position your variables so a temporary one is
declared just after pwm.

Example:

unsigned char pwm;
unsigned char i;

unsigned int var16 @ pwm;

Regards,

John Dammeyer



> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU] On Behalf Of Simon-Thijs de Feber
> Sent: Monday, April 08, 2002 11:01 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: [PIC]:PWM
>
>
> Hello All,
>
> Yesterday evening i have been struggling with a PWM
> function.
>
> A char should be loaded with e.g. 0xF0, afterwards
> rotated right, and every passing LSB should be put on
> a output pin.
>
> So i did this in CC5x
>
> led1 = pwm.0;
> pwm = pwm >> 1;
>
> this generates something like
>
> BTFSS pwm,0
> BCF   led1
> BTFSC pwm,0
> BSF   led1
> CLR   0x05, C  //clear carry
> RRF   pwm,1
>
> The clear carry is not required cause i want a
> continues rolling function.
>
> So i removed the "clear carry" in an inline assembly
> block and included that in my code, but that has not
> solved the problem.
>
> any one an idea ?
>
>
> grtz
>
> Simon
>
>
>
>
>
>
>
>
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