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#int_RDA and disable_interrupts()

 
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GIO
Guest
#int_RDA and disable_interrupts()
PostPosted: Thu Jan 11, 2007 4:36 am     Reply with quote
I am playing with my first completed PIC project from some week and I am happy but ....now I would to add rs232 comunication with PC

I have already read many post and think that better system is to use
#int_RDA for get character from rs232 but I have a function with a disable_interrupts(GLOBAL), this can to be a risk to garbage characters from PC?




Code:

//--------------------------------
// RS232 receive interrupt
#int_RDA
void RDA_isr()
//--------------------------------
{

rcv[len++] = fgetc(PC);

}


Code:

/------------------------
int16 ADC_CONV(int8 chan)
//------------------------
{
   #bit ADGO=0x1f.2           // ADC Status bit
   #bit ADON=0x1f.0           // ADC module on/off
   #bit ADIF=0xC.6            // ADC Interrupt Flag bit
   #bit PEIE=0xB.6            // Peripheral Interrupt Enable

   #byte ADRESL=0x9E
   #byte ADRESH=0x1E

   int8 Tmp;
   int16 Raw = 0;
   int16 min = 1023;
   int16 max = 0;
   int16 Value;


   set_adc_channel(CHAN);

   ADON=1;           // 1=ADC module is powered up, 0=ADC module is shut-off and consumes no operating current
   delay_us(20);     // Add a slight delay here the input capacitor will not be fully charged


   for (tmp = 0; tmp < ADC_NUMSAMPLES; ++tmp)
      {
      disable_interrupts(GLOBAL);    ///<<<<<<<<<<<
      enable_interrupts(INT_AD);

      PEIE=1;           // 1=Enables all unmasked peripheral interrupts, 0=Disables all peripheral interrupts

      ADIF=0;           // 1=ADC completed, 0=ADC is not complete

      ADGO=1;           // When ADON=1: 1=ADC in progress, 0=not in progress

      sleep();

      disable_interrupts(INT_AD);
      enable_interrupts(GLOBAL); //Note that these only need to be enabled at all
                                    //if you are intending to use another interrupt.

      Value = make16(ADRESH,ADRESL);
      Raw += Value;

      if (value <min> max)
         max = value;

      }

   Raw = Raw - (min + max);                  // tolgo i valori minimo e massimo
   Raw = Raw / (ADC_NUMSAMPLES - 2 );         // media delle letture

return (Raw);
}





Thanks in advance, GIO
Ttelmah
Guest
PostPosted: Thu Jan 11, 2007 6:22 am     Reply with quote
It'll depend on your chip, baud rate, and processor clock source.
Calculate how long an ADC conversion takes. This will depend on the selected ADC divider, clock rate etc.. On some chips, the master CPU clock can be left running, while the processor is asleep. If not, serial receive, will not take place at all (it is not disabling the interrupt that will then be the problem, but the fact that the UART clock will be stopped). If the clock can be left running, then provided the conversion time is less than a character time, there will not be a problem.
As an 'aside', you don't need all your fiddles with direct bit accesses.
read_adc(ADC_START_ONLY), triiggers the ADC to start. read_adc(ADC_READ_ONLY), reads the return. setup_adc(ADC_ON), tunrs on the ADC, while the same with 'ADC_OFF', turns it off. 'clear_interrupts(INT_AD)', turns off ADIF.
Aso, beware, that sleeping for a short time, may take a lot more time than you think. Check the oscillator startup times...

Best Wishes
ckielstra



Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands

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PostPosted: Thu Jan 11, 2007 7:31 am     Reply with quote
Just a thought, do you really need to disable the interrupts during the AD-conversion?
I guess you disable the AD-converter to minimize the noise induced by the processor? But, you are averaging the results, than assuming the induced processor noise is random the noise would not be visible in the result.
Guest
PostPosted: Thu Jan 11, 2007 10:02 am     Reply with quote
Reality, I have found this ADC_CONV() function on this (or another) forum and used after adding averaging the results.

I am beginner and I do not know if routine work also if I delete two rows:
disable_interrupts(GLOBAL);
enable_interrupts(GLOBAL);

or better use the simple value = read_adc()

In all case, I add other info on my project:

Code:

   #use rs232(baud=9600,parity=N,xmit=PIN_C6,rcv=PIN_C7,bits=8,stream=PC,errors)

   #include <16F877a.h>
   #device *=16
   #device adc=10
   #fuses WDT,HS, PUT, NOPROTECT, NOLVP
   #use delay(clock=10000000)

void main()
//--------------------------------
{
int8 restart_reason;

   restart_reason = restart_cause();

   setup_wdt(WDT_2304MS);
   restart_wdt(); // !!

   int_count = INTS_PER_SECOND;

   setup_timer_1 ( T1_INTERNAL | T1_DIV_BY_8 );
   set_timer1(3036);             // = 65536-(0,1/(4*4/10.000.000)) for 100ms

   setup_timer_2(T2_DISABLED,0,1);

   setup_adc_ports(RA0_RA1_RA3_ANALOG);
   setup_adc(ADC_CLOCK_INTERNAL);

   CLEAR_INTERRUPT(INT_RDA);
   enable_interrupts(INT_RDA);
   enable_interrupts(INT_TIMER1);
   // disable_interrupts(INT_TIMER2);
   enable_interrupts(global);





Thank to all,
GIO
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