Peter Koblauch

MC9S08QG8: 32.768Khz External Xtal or RTC - Current consumption?

Discussion created by Peter Koblauch on Jan 27, 2007
Latest reply on Jan 27, 2007 by Alban Rampon
 I am new to Freescal MCUs, what I know is just from reading the app notes and DSs.
 Coming from the msp430 with extremely low current consumption with an active RTC
 during "sleep" (msp430 LPM3 ~ Freescale stopx) I have been trying to understand if
 the same low current consumption (msp430F20XX: 500nA)  is  possible with Freescale MCUs.
 (I am not trying to promote the msp430 here, in fact I am considering a defection), so this
 thread was of great interest to me.
 However, the reason I am jumping in is the mentioning in the previous postings
 of the need for an external RTC IC.
 There is probably something I have missed here. It seems to me this is possible with just
 an external 32,768 kHz crystal on the MC9S08QG8 (16 pin version) EXTAL/XTAL pins?
The DS "MC9S08QG8 and MC9S08QG4 Data Sheet, Rev. 1.01" (page 264).
Current consumption during stop3 would then be around 6uA (3v).  
10x the msp430F20XX, but still so low that a coin cell battery, say CR2032,  would last 4-5 years,
which is acceptable (not great) for my application.
I hope somebody in-the-know in this news group could clarify this, e.g. for deep low current consumption, do
you need an external RTC IC or will a locally connected watch crystal do (if you can accept 6uA during stop3)?
Thank You
 Peter K
(Alban split to new post: new question = new post to ease clarity and search)

Message Edited by Alban on 2007-01-27 05:09 PM