Please Help Me With The Strange Problem---UPDATED

water_river · Joined: 17 Feb 2004 Posts: 16

hi, all,
I use PCW 3.094 and MPLAB 6.40 to program PIC16F877. The program is very simple:
//
#include <16f877.h>

#use delay (clock=20000000)
#fuses HS, NOWDT, PUT, NOBROWNOUT, NOLVP, PROTECT

void main(){

set_tris_b(0);

while (true)
output_b(0b11111111);
}
//
My programmer is MPLAB ICD2. All are going right, programming successfully and verifying program successfully, too, but there is no output, i.e, none of Port B pins goes high.
Can anyone tell me how to solve it??

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

There is a hidden SLEEP instruction placed at the end of main()
by the compiler. If you let your program run off the end of main(),
the PIC will to sleep. To avoid this, put a constant loop at the end.

void main()
{
set_tris_b(0);

while (true)
{
output_b(0b11111111);
}

while(1); // ADD THIS LINE
}

water_river · Joined: 17 Feb 2004 Posts: 16

It still doesn't work
I have checked the program memory selection. Under the self-selection mode, it programs from 0x0 to 0xB only. How come?
Then I use the manual selection and change it to full range, but it still doesn't work.

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

I made that post just as I was leaving work after an extended day.
Not wise.

Your code doesn't fall off the end of main(), because you have
a while() statement there. Even then, in sleep mode, the PIC
retains the state of the pins. So that's not the problem.

I would look closely at this:

water_river · Joined: 17 Feb 2004 Posts: 16

thank you in advance.
I'll wait for your reply

Ttelmah · Guest

water_river · Joined: 17 Feb 2004 Posts: 16

I am using the Demo board from Microchip, so there should not be any problem with hardware, i think.
In fact, when I use another compiler, PCM, it works.

Maverick · Guest

add this line after the #use delay...

#use fast_io(b);

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

I tested your code, as shown below, with PCM 3.094, and it worked OK.
I modified it slightly, to work with my bootloader, by reducing the
clock speed to 4 MHz. But that shouldn't matter.

I checked pins B0-B7 with my oscilloscope, and they were at a high
logic level.

So it likely is a hardware problem. Do you have anything
connected to the Port B pins ? If have an LED (or several)
connected to those pins, and you don't have series resistors
to limit the current, then this could cause the problem that
you're seeing.

water_river · Joined: 17 Feb 2004 Posts: 16

When I changed Port B to C, it still doesn't work.
Now I am using PCM, there is no problem.
But the problem is that I need to program PIC18F8720 in the project, although the C program would be almost similar.

water_river · Joined: 17 Feb 2004 Posts: 16

hi, all,
With the same C program:
//
#include <16f877.h>

#use delay (clock=20000000)
#fuses HS, NOWDT, PUT, NOBROWNOUT, NOLVP, PROTECT

void main(){

//set_tris_b(0x00);

while(true)
output_b(0b11111111);
}
//
using two CCS compiler to program, I view the program memory and find it written differently:

in the case of using PCM:
MOVLW 0
MOVWF 0xa
GOTO 0x4
NOP
CLRF 0x4
MOVLW 0x1f
ANDWF 0x3, F
MOVLW 0x9f
MOVWF 0x4
MOVLW 0x7
MOVWF 0
MOVLW 0
BSF 0x3, 0x5
MOVWF 0x6
MOVLW 0xff
BCF 0x3, 0x5
MOVWF 0x6
GOTO 0xb
SLEEP
ADDLW 0xff
...
INCF 0, W (end memory)

in the case of using PCW:

MOVLW 0
MOVWF 0xa
GOTO 0x4
NOP
CLRF 0x4
MOVLW 0x1f
ANDWF 0x3, F
MOVLW 0xf
BSF 0x3, 0x5
ADDLW 0x9f
ADDLW 0xff
...

Obviously, the one done by PCW does not work.
Do any know why??