madness setting in!

[davt]

Hi all

Compiler version 3.210.
Pic 16F767.
Programmer Warp-13


If I program my 16F767 with the code below which continually sets the test pins high - all pins should remain high!!

But what I am seeing are pulses 0.2us wide and 2us spacing on pins portb.1 to portb.4

void main(void)

{

trisa=0b00000111;
trisb=0b00000000;
trisc=0b10000000; // set rc7 rx as an input


test0=0; //
test1=0; // oscilloscope
test2=0; // test
test3=0; // pins
test4=0;
test5=0;
test6=0;
test7=0;

gie=0; // disable all interrupts


while(1)

{

test2=1;
test3=1;
test4=1;
test5=1;
test6=1;
test7=1;

}

}

If I alter the code to:

void main(void)

{

trisa=0b00000111;
trisb=0b00000000;
trisc=0b10000000; // set rc7 rx as an input


test0=0; //
test1=0; // oscilloscope
test2=0; // test
test3=0; // pins
test4=0;
test5=0;
test6=0;
test7=0;

gie=0; // disable all interrupts


while(1)

{

portb=0xff; // sets all pins high

}

}

All the pins remain high - as they should!

This only happens on a 16F767

Am I missing something???????

Dave

[SherpaDoug]

It sounds like a read-modify-write problem. Try adding a 1ms delay between setting each pin high:

test2=1;
delay_ms(1);
test3=1;
delay_ms(1);
test4=1;
delay_ms(1);
test5=1;
delay_ms(1);
test6=1;
delay_ms(1);
test7=1;
delay_ms(1);

and see if the problem goes away. The root of the problem is the structure of the PIC output pin and its connection to the CPU, there is nothing the compiler can do about it. If two commands to modify a port are in the instruction pipeline together, the first one may be lost. A short delay (1us is probably enough depending on your clock speed) lets the first command complete before the second starts, so everything works.
I am sure there many references to this "gotchya" on this BBS and any other PIC related source.
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[Mark]

[asmallri]

What about adding

[SherpaDoug]

[Mark]

It could actually make it worse. With standard IO the tris register are set/cleared with takes additional instruction cylcles with actually adds a small amount of delay.

[Guest]

How did you declare

test0 to test7 ?