Switching the clock source

[idakota]

I'm struggling to get the micro to switch its clock source.

I've got a 10MHz external crystal so to use the PLL I need to modify the PLLPRE and PLLPOST bits. Following the setup guidelines from microchip tells me that I need to modify the values and then switch from the internal RC (for example) to the external crystal with PLL.

Using the microchip supplied code to switch clock sources produces the following error: "Invalid ASM instruction(135): #OSCCONH"

The ASM code is:

Code: Select all

   asm {
        ;Place the New Oscillator Selection (NOSC=0b011) in W0
        MOV #0x13,W0
        ;OSCCONH (high byte) Unlock Sequence
        MOV #OSCCONH, W1
        MOV #0x78, W2
        MOV #0x9A, W3
        MOV.B W2, [W1] ; Write 0x78
        MOV.B W3, [W1] ; Write 0x9A
        ;Set New Oscillator Selection
        MOV.B W0, [W1]
        ; Place 0x01 in W0 for setting clock switch enabled bit
        MOV #0x01, W0
        ;OSCCONL (low byte) Unlock Sequence
        MOV #OSCCONL, W1
        MOV #0x46, W2
        MOV #0x57, W3
        MOV.B W2, [W1] ; Write 0x46
        MOV.B W3, [W1] ; Write 0x57
        ; Enable Clock Switch
        MOV.B W0, [W1]
wait:
             BTSC OSCCON, #0
             BRA wait
   };

Any help would be appreciated!

[rmteo]

When using embedded ASM, this applies to mikroBASIC:

If you plan to use a certain mikroBasic variable in embedded assembly only, be sure to at least initialize it (assign it initial value) in mikroBasic code; otherwise, the linker will issue an error. This is not applied to predefined globals such as PORTB.

Should be the same in C. I usually do this before the ASM code:

Code: Select all

OSCCONH = OSCCONH
OSCCONL = OSCCONL

[idakota]

Thanks, but it doesn't work.

OSCCON is a SFR for the PIC24s. I think that OSCCONH stores the address for the high byte of OSCCON and OSCCONL stores the address for the low byte in the Microchip compiler. Obviously mC does not share these values.

Edit: I got it working by replacing OSCCONL and OSCCONH by the absolute addresses for the low byte and high byte of OSCCON