Problems with RS232 and internal oscillator (PIC16F688)

[mtar]

I've a problem with internal oscillator and the serial port of PIC16F688. When I use the external oscillator (8MHz), I can send from PIC normally with a velocity of 9600bps. When I don't connect the external quartz and relative condenser and I use the internal oscillator with this istructions:

#FUSES NOWDT, INTRC_IO, NOPROTECT, BROWNOUT, NOMCLR, NOCPD, NOPUT, IESO, FCMEN
#use delay(clock=8000000)
...
setup_oscillator( OSC_8MHZ );

I receive in Hyperterminal only byte 00.

I have tried to change the frequency to 4Mhz or to decrease the serial speed to 1200 and 2400, but the problem remains.

I use the PCWH 3.227 and MPLAB 7.21.

Thanks.

M.

[PCM programmer]

Post a complete (but short) test program that demonstrates the problem.

[Guest]

Okay, this is the code for PIC16F688.
Thank you for your help!! M.

-------------------------------------------------------------------
Main firmware
-------------------------------------------------------------------

#include "C:\Programmi\PICC\acceleration.h"
#define INTS_PER_SECOND 30 // (8000000/(4*256*256))
BYTE int_count; // Number of interrupts left before a second has elapsed

// variable for the X Axis of accelerometer
float x;

// interrupt of 1 Hertz in order to send the X value of accelerometer
#int_rtcc
void clock_isr() {
// decrese and check the counter interrupt (for 1 Hertz)
if(--int_count==0) {
//reset counter
int_count=INTS_PER_SECOND;
// send accelleration data
printf("x,%0f\n\r",x);
}

}


void main() {
int value;

//----------------------------------------
setup_oscillator( OSC_8MHZ );
int_count=INTS_PER_SECOND;
set_timer0(0);
setup_counters( RTCC_INTERNAL, RTCC_DIV_256 | RTCC_8_BIT);
enable_interrupts(INT_RTCC);
enable_interrupts(GLOBAL);
setup_adc_ports(sAN4|sAN5|sAN6|sAN7|VSS_VDD);
setup_adc(ADC_CLOCK_INTERNAL);
setup_comparator(NC_NC);
setup_vref(FALSE);
setup_oscillator(False);
//----------------------------------------

// value Volts converter (3.3V / 255 sample)
reference = 0.012941176;

// wait mechanical stabilization of sensor
delay_ms(4000);


// loop A/D
do {
// sample the x axis
set_adc_channel( 4 );
delay_us(10);
value = Read_ADC();
// convert to volts
x = (float)reference * (float)value;

// here there are other Axis...
// .....

delay_ms(10);
} while (TRUE);
}



-------------------------------------------------------------------
accelleration.h
-------------------------------------------------------------------

#include <16F688.h>
#device adc=8

#FUSES NOWDT //No Watch Dog Timer
#FUSES INTRC_IO //Internal RC Osc, no CLKOUT
#FUSES NOPROTECT //Code not protected from reading
#FUSES NOBROWNOUT //No brownout reset
#FUSES NOMCLR //Master Clear pin used for I/O
#FUSES NOCPD //No EE protection
#FUSES PUT //Power Up Timer
#FUSES NOIESO //Internal External Switch Over mode disabled
#FUSES NOFCMEN //Fail-safe clock monitor disabled

#use delay(clock=8000000)
#use rs232(baud=9600,parity=N,xmit=PIN_C4,rcv=PIN_C5,bits=8)

[PCM programmer]

The line in your program shown below in bold should be removed.

[Guest]

Incredible, I was not really realized to have written again that istruction. That's why it worked only with the external oscillator… Thank you very much and excuse me for the ingenuity of this error…


Best regards
M.