voltage and delay problem

[trento]

HI Dear all

I work with 16F877 PIC .My problem is when I programed the PIC to give 8 square wave signals at frequency 50HZ with different delay between each others .when I checked by oscilloscope the frequency and delay ware not as I programed and the peak voltage was 2.5 volt so please tell me what is the problem .

regardes
[/code]

[kender]

Do you have anything connected to the pin? How much current are you sinking fom the pin? There might be something holding the line down, like a relatively small resistance connected between the pin and ground. The resistance could be a solder bridge.

[trento]

thank u for replay . there is nothing conected with bin i just measure directly from the bin by the oscilloscope and waht about the wrong on the frequency i use delay function and use delay with speed 20000000

[asmallri]

[trento]

thank u for ur response i will send my code to you now

[trento]

[/****************************************************
* *
* COPYRIGHT (c) safoan *
* *
* codes = Chasing signal *
* *
* KIT = emBox-877 Kit ( CPU = PIC16F877A ) *
* *
* STATUS = DONE 12/09/05 *
* *
****************************************************/
#include <16F877A.h>

#FUSES HS,NOWDT,NOPROTECT,NOPUT

#USE DELAY( CLOCK=20000000 )

#byte port_a=5 /* define the address of PORTA */

#byte port_b=6 /* define the Address of PORTB */

#byte port_c=7 /* define the address of PORTC */

#byte port_d=8 /* define the address of PORTD */


static byte CONST UP_MAP[8] = { 0x01,0x03,0x07,0x0f,0x1f,0x3f,0x7f,0xff };

static byte CONST DOWN_MAP[8] = { 0xfe,0xfc,0xf8,0xf0,0xe0,0xc0,0x80,0x00 };

static byte CONST delay_v[8] = { 365,1145,998,950,950,998,1145,365 };


/***************************************
* LED wiring *
* ********** *
* 8 signals = PB0 - PB7 *
* 8 signals = PD0 - PD7 *
***************************************
* NOTE: see emBox-877 schematic *
***************************************/


main(){


char cnt,tnt;

/* long asof;*/

/* set_tris_a(0xfe); */ /* set port_a to be RA0 outputs */

set_tris_b(0); /* set port_b to be ALL outputs */

/* set_tris_c(0xbf); */ /* set port_c to be RC6 outputs */

set_tris_d(0); /* set port_d to be ALL outputs */



/* tnt = 0 ; */ /* intialize counter tnt */


port_b = 0 , /* initialize & turn off ALL PORTB outputs */


/* port_c =0; */ /* initialize & turn off ALL PORTC outputs */


port_d = 0xff; /* initialize & turn on ALL PORTD outputs */



for(;;){ /* forever loop*/


/* if(tnt == 80)


tnt = 0 ;


if (tnt % 2 == 0) */ /* multiplixer condition selector */


/* port_a = 0x01, port_c=0;


else port_c = 0x40, port_a=0;*/


DELAY_US (delay_v[0]) ;


for (cnt=0 ; cnt < 4 ; cnt++) { /* delay loop for the first H-bridge leg (positive cycle) */


port_b = UP_MAP[cnt],

/* pick value to display from array */
port_d = 0xff - UP_MAP[cnt];


if (cnt==3)


DELAY_US(3084);


else DELAY_US(delay_v[cnt]+1); } /* delay time loop for increment stage (positive cycle)*/


for( cnt=4 ; cnt < 8 ; cnt++ ){ /* delay time loop for decrement stage (positive cycle) */


port_b = UP_MAP[cnt] ,


port_d = 0xff - UP_MAP[cnt];


DELAY_US ( delay_v[cnt] ) ; }


/* if(tnt == 80)


tnt = 0 ;


if ( tnt % 2 == 0 )


port_c = 0x40 ,


port_a = 0x01 ;


else port_c = 0 ,


port_a = 0 ;


tnt++ ;*/


DELAY_US( delay_v[7] );


for (cnt=0 ; cnt < 4 ; cnt++) { /* delay time loop for increment stage (negative cycle) */


port_b = DOWN_MAP[cnt] ,

port_d = 0xff - DOWN_MAP[cnt];


if (cnt==3)


DELAY_US(3084);


else DELAY_US(delay_v[cnt+1]);}


for (cnt=4 ;cnt < 8; cnt++){ /* delay time loop for decrement stage(negative cycle) */


port_b = DOWN_MAP[cnt],

port_d = 0xff - DOWN_MAP[cnt];


DELAY_US( delay_v[cnt] );

}


}
}





][/code]

[Ttelmah]

First, when you post code, use the 'code' button, otherwise it is almost unreadable to us.
Second remove 'remmed' out lines which also make the program flow almost unreadable.
Comments though, on the glaring faults. A _variable_ used in a delay statement can only be an integer. Hence 255 max.
Even if this was not the case, you are trying to store values over 255, into an integer variable.
Your delays will be completely screwed.
On the 2.5v question, double check that your scope is set to the range you think it is, and try a simple test, just toggle a line high/low, with no other code. Also note that you should be disabling the peripherals that exist on some of the IO pins being used, or may get unexpected results. Look at the typical initialisations used on code posted, or use the wizard (which will generate some unecessary initialisation, it will show the sort of extras needed.

Best Wishes

[Mark]

[trento]

when i cahange the defination of matrix also there is no cahnge I put long and int16b even float there is no change

[Ttelmah]

[trento]

thank you so much for your care I tried your suggestion it work properly .

But I want to use the matrix because I want to store groupe of delay

angle sets.Depending on the feedback ,one of the sets will excute I do

single phase induction motor control using PIC this programe just one

set of angle from my program please tell how I can do it .

regards.

[Ttelmah]

Write your own delay function that accepts a larger variable. You don't say how fast the processor is running, which will affect both the accuracy, and limitations on this. You could also consider using the CCP, to give a much more accurate result. If you run timer2, so it has the longest period you require, then you can program the CCP, to the period you require, clear it's interrupt flag, and just 'poll' this till it changes, to get accurate timings.

Best Wishes

[Mark]

How accurate do the delays need to be?
You will most likely need to write you own delay routines or wrap the built in delay routine inside your own function. You could put a delay_us(256) inside a for loop and execute it multiple times. Each time subtracting 256 from your delay value until the value is less than 256 and then call one final delay with the result. Keep in mind that loops and conditional tests take time so you can adjust for this by delaying less than 256 to compensate for the added overhead of the loop.

[trento]

Thank u so much it was very good hints thank you for your help

[PCM programmer]