This is a snippet of start up code for a PIC24EP256MC204 project I have been working on....( FRC oscillator switching to FRC+PLL). it works fine.... until I wanted to count seconds from a DS1338 .. I found out a couple of hours ago, it stops Timer 1 from counting using the T1CK input pin … This PIC does not have RTCC so no secondary oscillator, but it seems the bit (1) in OSCCON to enable it is still active (red text) , enabling the SOSC interferes with the T1CK input, my mistake was to paste the code from a 24F device with RTCC and I had not appreciated the difference … thought I would share my head scratching.
PLLFBD = 33; //M CLKDIVbits.PLLPOST = 3; // N2 CLKDIVbits.PLLPRE = 0; // N1 __builtin_write_OSCCONH(0x01); // Initiate Clock Switch to FRC oscillator with PLL (NOSC=0b001) __builtin_write_OSCCONL(OSCCON | 0x03); // Enable Switch & sec osc (PIC24F ! ) __builtin_write_OSCCONL(OSCCON | 0x01); // Enable Switch while (OSCCONbits.COSC != 0b001);// Wait for Clock switch to occur while (OSCCONbits.LOCK != 1);// Wait for PLL to lock // REF CLOCK IS PIN 8 - RB10 // FSC and PLL now at 16Mhz OSCTUN = 0x0030; // TUNE +- 8MhzOSC ---- end of snippet ---