ST7Lite29 - internal RC oscillator adjustment

[wolfgang2399]

Posted on August 17, 2005 at 06:09

ST7Lite29 - internal RC oscillator adjustment

[wolfgang2399]

Posted on July 26, 2005 at 08:17

Hi,

is there anybody who can help me calibrating the internal RC-oscillator of the Lite29? In my approach to the problem I found out a unexplainable phenomenon.

- The problem:

According to AN1324 I am trying to calibrate the RC oscillator measuring a defined interval (20ms @ 50Hz) and successive reloading the RCCR.

--> Sometimes the new values stored at RCCR don't cause any effect, sometimes the result is o.k.

There is no advancement when I wait for about 100ms (without reset) after each change of RCCR before I take a new sample.

Restarting the micro after each change brings the assumed effect.

Any idea??

Thanks

WoRo

[fggnrc]

Posted on July 26, 2005 at 10:24

WoRo,

the RC oscillator frequency depends not only on RCCR value, but also on temperature, supply voltage, ...

For this reason a small change may cause no effect (as are the ones that you observed).

After a reset, the RCCR is set to $FF, i.e. the slowest frequency. Therefore the value you write in RCCR causes a measurable effect.

If you need more control on RC oscillator, why do not you implement a software PLL: measure the actual frequency, compute the error and adjust accordingly the RCCR. This solution however needs the continuos availability of the reference signal, and I do not know if it fits well in your application.

Regards,

EtaPhi

[wolfgang2399]

Posted on July 26, 2005 at 12:09

EtaPhi,

thank you for your answer.

*******

... the RC oscillator frequency depends not only on RCCR value, but also on temperature, supply voltage, ...

*******

The fact is, that temperature or supply effects I can surely disregard. Because the timings of both procedures are nearly identical.

Only, at the faulty one I set RCCR with the new value but don't reset the micro but with the successful procedure I add a reset after each new voting (RCCR is copied to EEPROM_RCCR_5V).

The time between two samples is about 150ms - in both cases.

*****

If you need more control on RC oscillator, why do not you implement a software PLL: measure the actual frequency, compute the error and adjust accordingly the RCCR.

*****

Tracing the samples shows me that sometimes there is no change in the frequency when changing RCCR without resetting the micro.

Furthermore I calibrate my RC in a test control unit and only there I generate the 20ms signal. In my final device there is no such a signal.

Best regards

WoRo

[mustapha_jellouli]

Posted on August 16, 2005 at 14:41

Dear Woro,

About the calibration AN1324, I met some problems which I can not explain.

I use this application every hour , and sometimes the micro stucks. Do you have the same problem?

So I used another application which I developped.

Regards

Mustapha

[wolfgang2399]

Posted on August 17, 2005 at 06:09

Hi Mustapha,

seems so!

I can't explain the effect, that sometimes setting a new value to the RCCR does not change the frequency. Only, each time when I set RCCR after a reset the new value has been taken into account.

But the micro didn't stuck at all...

By the way: Where are the :o ST application engineers or our :o Moderator helping us with solving our/their problems!!

Where can we find information about known malfunctions?

Best Regards

WoRo