MC9S08QB4; Using a 100kHz external low-power crystal in FBELP mode, but can not find recommended information

Discussion created by Guest on Apr 17, 2013
Latest reply on Apr 21, 2013 by Brambostel

Hi Guys, I'm still having a little problem in timing/clocking this µC in Ultra-Low-Power Mode.

Short background: trying to set an output-pin (at PTB) as fast as possible, on-state to off-state within 60µs (or a bit less) in FBELP. This is not possible with a 32,768kHz crystal on XTAL/EXTAL. I'm using assembler for faster execution, but the shortest interval I can program is 250µs. Even if I use a 38,4kHz crystal to shorten interval (on-/off-state) I can not reach 60µs, it's 130µs. I already tried 100kHz as external crystal and it is running fine, but...

Now my little problem and question: datasheet, manual, CodeWorrier and application notes don't even say it is possible to use an 100kHz external crystal in FBELP. Maximum is 38,4kHz.

e.g. AN3499 “Clock Options on the HC9S08 Family“ don't even borders the device MC9S08QBx but concerning the family?! Nice!

I realy need a suitable statement.

Any helpful ideas??? Thanks for answering.


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