There are a dozen possible causes.  It is useful to list some of the ones
that have  caught me:

1.  Defining two variables to the same memory location, then wondering why
one of them changes seemingly randomly

2. Partial Resets due to noise on the MCLR line not completely resetting
the PIC and leaving it in an unknown state

3.  EMI noise from an adjacent relay changes PIC registers

4.  Unexpected  WDT reset due to not putting WDT reset statements in
proper places

5. Timer interrupts not behaving as I thought they would due to
thumb-fingered programming of TIMERH and TIMERL registers

6. In assembler, messy stack issues when an interrupt trashes a key
register like w  (C compilers are supposed to deal with this
auto-magically)

7.  Leaving undefined states in any area of the program.  For example:

        char i;
        i= 10;
        do{
                some stuff
        }while(i--);

is perfectly acceptable in C Programming 101 but does not define behaviour
if noise or programming pencilheadedness enters the loop with I = 254.

        char i;
        i= 9;
        do{
                some stuff
        }while(--i < 9 );

will define behavior for every possible value of i.

 8.  Ground bounce due to motors, inductive loads, or other heavy loads on
same ground bus as PIC, inadequate grounding and PCB layout

9. Fried PIC pins.  The plucky PIC will still run after a bus fight  has
destroyed two or three I/O pins, as long as they aren't shorted.


And the top 10 reason for this behaviour is:

10.  Dumb programming mistakes.  Pick apart your program pretending that
your worst enemy wrote it and you have to prove he is an idiot to win a
million bucks.  You will find the problem very quickly.

I have done all of these and spent a half a day each on them until I went
"D'OH" and figured them out.

Tell us a little more detail and we can help you more specifically.


-- Lawrence Lile





paul sayuj <paul_sayuj@YAHOO.CO.IN>
Sent by: pic microcontroller discussion list <PICLIST@MITVMA.MIT.EDU>
10/25/2003 02:10 AM
Please respond to pic microcontroller discussion list


        To:     PICLIST@MITVMA.MIT.EDU
        cc:
        Subject:        PIC:weird jump of program to other program memory location


 hi,
I am facing a frustrating problem.
 My program is jumping to other program location not
according to the flow of program.what may be the cause
of it?

paul sayuj


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