PIC24F secondary oscillator

[lindermat]

Hi all,
I've searched the forum and can't seem to find an answer to my problem. In my design using a PIC24FJ256GB210 and are using both the primary and secondary oscillator. The primary oscillator (24Mhz crystal) works fine, but I can't get the secondary one to work.

I am using a 32.763kHz tuning fork crystal with 12.5pF load caps. It's connected to the SOSCI and SOCSO pins. The first problem (which may be why it's not working) is that when I probe the pins the signal is small compared to the primary oscillator. It's only about 1 volt p-p. If I don't enable it using the fuse command or just turning on the RTCC I don't get anything so I know the OSCEN bit is being set. I can also change the drive level to low and see the amplitude reduce.

I know the program logic is correct because if I change to the internal osc from sec secondary one it works (but the timeout is much faster)

Any thoughts/suggestions?

Thanks

[FvM]

The secondary oscillator is low power and most likely has a lower level by design. I also guess, it's considerably reduced by a standard oscilloscope probe. You don't use a low capacitance active probe?

I rather suspect a software proble, either in your code or CCS built-in function. Without a compilable code example and knowledge of the CCS version, nothing can be done.

[temtronic]

quick comment.

While I don't use the 24 series, odds are they generally have the same 'internals' as the 18F4550, which I know works fine with the 32KHz xtal as the seconadary .
Probably a 'setup' issue. Try a very simple program(blinking LED 1 Hz rate).Dump the listing,compare to datasheet to confirm the proper bits are being configured.

[lindermat]

Thanks for the input, I think my problem is that I'm trying to use timer4 and I don't think it can be configured to use the secondary oscillator, only an external pin, or the internal main oscillator.

Is this correct?

[temtronic]

Download the datasheet, look at the 'figures' to see the possible configurations allowed.
Sometimes I find it easier to look at the pictures to see the 'flow' of signals instead of reading pages of specs.( yeah, I'm getting old.....)

[bkamen]

[lindermat]

OK, I'll use timer 1 with the external crystal, but I need to start and stop the timer. In the datasheet there is a bit called TON that it looks like I can use to do this, but I can't see how to control it using the CCS functions.

Do I have to access it directly or can I use setup_timer1(TMR_DISABLED) to turn it off? I don't want to reset or reconfigure it, just start and stop it based on events in my program.

Thanks,

[bkamen]

[FvM]

setup_timer1(TMR_DISABLED) resets all TCON bits, e.g. prescaler settings. You should control TON bit selectively to start and stop the timer.