MC9S08QG8 Timer in Stop Mode

[Rhioponomous]

Hi All,
 
Is there a way to enable the timer so it keeps a count while in stop3? I need to maintain a count of the time between triggered ADC interrupts while the MCU is in stop3.  I would very much appreciate any help in this regard as I am very new.

Thanks!

[bigmac]

Hello, and welcome to the forum.

You would need to use the RTI module to periodically wakeup the MCU, increment a counter variable in RAM, and then re-enter STOP3 mode.  With this method, the timing resolution will be about 8ms minimum.

For timing accuracy, you would need to use an external crystal as the clock source, rather than the internal 1kHz oscillator.  The external clock will need to be enabled during STOP3.

Regards,

Mac

[oudeis]

I'm trying the exact same thing on an MC9S08RD60/MC9S08RG60, but I can't figure out how to enable it. The data sheet says (section 5.7):

---

When using the external oscillator in stop3 mode, it must be enabled in stop (OSCSTEN = 1) and configured for low bandwidth operation (RANGE = 0)[/quote]

---

But I can't find any reference to OSCSTEN. Currently, my timer is configured to generate an interrupt every 1.11 ms (with 15MHz crysta, RTIS is set to 1:1:0, equalling 'T_ext x 1638'). Do I need to change anything to the timer configuration to keep it running when entering stop3 mode?

Regards,

Ruud

Message Edited by oudeis on 2009-03-24 07:42 AM