Cannot get PIC16F747 to run with internal oscillator

[fsimjee]

I have been able to run my PIC16F747 with an external 20MHZ crystal. Now when I change the oscillator setting from HS to INTRC or INTRC_IO in the #fuse command line, the PIC will not run. I even set OSCCON to 0x74 without any luck.

With the same OSCCON setting, I was able to run the PIC with the CC5X compiler and the internal oscillator without any problems. It looks like there is some bug in the compiler.

The compiler version is 3.181 if that helps.

Here is my code:

test.c:
#include "test.h"

#use delay(clock = 8000000)

void main()
{

OSCCON = 0x74;

setup_adc_ports(NO_ANALOGS);
setup_adc(ADC_OFF);

set_tris_A(0);

while(1)
{
OUTPUT_A(0xFF);
delay_ms(200);
OUTPUT_A(0x00);
delay_ms(200);
}

}


test.h:
#include <16F747.h>
#device *=16
#device adc=8
#use delay(clock=20000000)
#fuses NOWDT,INTRC_IO, NOPUT, NOPROTECT, BROWNOUT, BORV20, NOMCLR, NODEBUG
#use rs232(baud=9600,parity=N,xmit=PIN_C6,rcv=PIN_C7,bits=9)
#BYTE OSCCON = 0x8F

[PCM programmer]

The first thing I would do is make a test program that's not split up
into two files. See below.

The main problem is that your version of the compiler is buggy for
the 16F747.

1. In the code that occurs right after the reset vector (at 0x0000), it's
calling location 0xFFF. Then it puts W into OSCCON.
This is wrong. I think when CCS saw an OSCCON register,
they thought it was an OSCCAL register as in the 12F675, and
treated it in the same way. Here's part of the .LST file.
The code appears to call 7FF, but it's actually FFF because of
the value loaded into PCLATH right before that.

[fsimjee]

Thanks a lot! Worked like a charm!