ICSP not recognizing..

[sirvo]

Hello..

I've implemented the ICSP and it's working really fine.. BUT, the winpic800 do not recognize the 16f877 at the second time, neither at the thirty... I got to remove pic from the board, disconnect the device and restart.... then it works...

Have anyone the idea of what is going on?

Thanks in advance..

[mackrackit]

Is the software set up to erase before programming?
And what are you doing with MCLR?

[sirvo]

Yeap..

I always erase pic after programming and MCLR is tied like this:

VCC-10K-1N4148-MCLR-VPP(ICSP)

Thanks!!

[mackrackit]

Does it always work the first time?
Try adding capacitors between VDD and VSS. As close as you can to the PIC on both sides. I had a similar problem once with the PICSTART and an 18F'r. ???

[sirvo]

Well, I've tried that too... same thing..

Sometimes it works on the second try... i do not know..

Well, got another problem, could you help again???

I'm trying to make TMR1 interrupt at 36kHz.

It uses a 20Mhz crystal... The code is below:

@ DEVICE pic16F877, HS_OSC ; System Clock Options
@ DEVICE pic16F877, WDT_OFF ; Watchdog Timer
@ DEVICE pic16F877, PWRT_ON ; Power-On Timer
@ DEVICE pic16F877, BOD_OFF ; Brown-Out Detect
@ DEVICE pic16F877, CPD_OFF ; Data Memory Code Protect
@ DEVICE pic16F877, PROTECT_OFF

define OSC 20 

INT       VAR     PIR1.0  ' OVERFLOW flag
START   VAR     T1CON.0 ' START TMR1
LOAD     VAR     word

'------- Configurações iniciais -------------------- 
TRISA  = %00000000 ' PORTA
TRISB  = %00000000 ' PORTB 
TRISC  = %00000000 ' PORTC
TRISD  = %00000000 ' PORTD 
TRISE  = %00000000 ' PORTE 

INTCON = %11000000  ' enable global interrupt
OPTION_REG = %00000000
ADCON1 = %10001111  ' all digital
T1CON = %00000000   ' TMR1 1:1 prescaler
PIE1 = %00000001    ' Henable  TMR1 INT
START = 0
INT = 0
LOAD = 65404 '  INT. 36KHz
'--------------------------------------------------- 
ON INTERRUPT GOTO SINUS

TMR1L = LOAD.lowbyte
TMR1H = LOAD.highbyte
START = 1 
PORTB.0 = 1
MAIN:      
        GOTO MAIN    

 
DISABLE
SINUS:  INT = 0
           TMR1L = LOAD.lowbyte
           TMR1H = LOAD.highbyte
           PORTB.0 = 1 ' JUST TO MEASURE THE FREQ. ON OSCILLOSCOPE
           PORTB.0 = 0
RESUME
ENABLE

end

The oscilloscope do not shows 35.9kHz, but 30~33kHz...

Anything I can do?

Thanks again!

[mister_e]

make sure you also disable the LVP mode. This pin have to be loaded to GND when progaming.


And then... when you reload a 16Bit timer you want to add the reload value instead of just dumping the values in. Finally you want to stop it, then add the reload value, the restart the timer.

Depending how accurate you want it, not a bad idea to switch to Darrel's instant INTs (PBP or ASM... where asm is always handy .. )

[skimask]

Try this and see what happens, should give you a 50% duty cycle ~36khz square wave on your o'scope:

@ DEVICE pic16F877, HS_OSC ; System Clock Options
@ DEVICE pic16F877, WDT_OFF ; Watchdog Timer
@ DEVICE pic16F877, PWRT_ON ; Power-On Timer
@ DEVICE pic16F877, BOD_OFF ; Brown-Out Detect
@ DEVICE pic16F877, CPD_OFF ; Data Memory Code Protect
@ DEVICE pic16F877, PROTECT_OFF
DEFINE OSC 20
load con 65468:intcon=$c0:option_reg=0:adcon1=$87:t1con=1:pie1=1:c var byte
goto main
ON INTERRUPT GOTO SINUS
TMR1L=LOAD.lowbyte:TMR1H=LOAD.highbyte
MAIN:      GOTO MAIN    
DISABLE
SINUS: if pir1.0=1 then
          pir1.0=0:tmr1l=load.lowbyte:tmr1h=load.highbyte:c=c+1:portb.0=c.0
          endif
RESUME
ENABLE
END

And take note of Mr_E's note about adding values.