Problem with strange PIC behavior

[mrcube_ns]

Strange PIC behavior

Here some small test in Hi te ch Pi cc mcu is 16f628.

Here is code:

#include <pic.h>
//#include <pic1662x.h>
#define PORTBIT(adr, bit) ((unsigned)(&adr)*8+(bit))
//__CONFIG(CP1|CP0|CPD|FOSC2|FOSC0|WDTE);
static bit test @ PORTBIT(PORTB, 1);
unsigned int i;


void main (void)
{
TRISA = 0;
TRISB = 0;
PCON = 0xFF;
OPTION=0x40;
INTCON=0x90;

PORTA = 255;
PORTB = 255;

test=1;

while(1){
if(test == 0)
test = 1;
else
test = 0;

for(i=0;i<10000;i++){
}//for
}//while
}//main


Here is what I see on oscilloscope on test pin non simetrical square signal :


___| |________________________| |_________________________



Any ideas?

Is it something wrong with code, am I doing something wrong???


Mr.Cube

 

[socketz]

Re: Strange PIC behavior

It probably has to do with what instructions the compiler generates for the while loop, there probably is a GOTO involved (which takes 2 cycles).
If you need perfect timing better do it in MPASM and count the clock cycles for each instruction.

 

[E-design]

Re: Strange PIC behavior

You can get strange things with the 628 if you don't disable the comparator functions when you are not using them!



ASM

movlw b'00000111' ; disable comparators
movwf CMCON

 

[Humber555]

Re: Strange PIC behavior

Hi mrcube_ns,

1)

//__CONFIG(CP1|CP0|CPD|FOSC2|FOSC0|WDTE);

Not HiTe user but it seems that you have the WDT enable.


2)
unsigned int i; // This is an 8 bit integer whose max val = 255

Then in the for loop, the conditional test is expecting something imposible.

for(i=0;i<10000;i++) // i < 10000 ??????



Hope this help you.

Regards,


Humber555

 

[C-Man]

Re: Strange PIC behavior

mrcube_ns,

as you do not use PORTA you can leave the comperators enabled without problems.

Your problem is that you have enabled the watchdog and do not reset it.

Put this:

asm("clrwdt");

in you for loop and you should get wat you want

best regards

 

[mrcube_ns]

Re: Strange PIC behavior

You can get strange things with the 628 if you don't disable the comparator functions when you are not using them!

Good to know that comparators can make trouble sometimes.

2) 
unsigned int i; // This is an 8 bit integer whose max val = 255 

Then in the for loop, the conditional test is expecting something imposible. 

for(i=0;i<10000;i++) // i < 10000 ??????

Humber555
integer is number between 0-65535 if it's defined as unsigned int value, so 10000 is very good int value (signed or unsigned no mater).


C-man tnx for answer, good point. But I deactivate WD option in programmer software (SW:ic prog, HW: propic2 programmer). Maybe software dont disable WD ?!!? All try to reset WD in while loop and see result.

Mr.Cube

 

[SphinX]

Strange PIC behavior

Hi Humber555

unsigned int i;
for(i=0;i<10000;i++)

These statments are vaild becuase

int i takes 2 bytes from -32768 to +32768
unsigned int i removes the signed and add them to the positive (i will value between 0 : 65535)

But

char i take 1 byte ( -127 to 128)

and so

unsigned char ( 0 -255)

SphinX

 

[Humber555]

Re: Strange PIC behavior

Sorry, my mistake because I had been working with NO ANSI compliance
C Compiler, where
unsigned int size is 8 bit (255)

humber555