RTC-Pins LPC122x and EAGLE library

lpcware · ‎06-15-2016

Content originally posted in LPCWare by Caradhras on Thu Oct 18 02:55:54 MST 2012
Hi,

i wonder, what can be done with the RTC-pins of the LPC122x with LPQFP48-package. (RTCXIN and RTCXOUT)

The chapter 16 of the UM does not mention the pins and states, that the clock for the RTC is derived from the main clock or from the built in RTC oscillator.

Additionally no information is given about the accuracy of the builtin RTC oscillator. :( Is it precise enough to keep the time over month of operation? Like in a real clock?

Unlike the LPC11Cxx NXP does not provide CAD-models for the LPC122x, I made an EAGLE lbr for the LQFP48-versions. Use it if you want for whatever you want. :) If you find errors, tell me!

https://dl.dropbox.com/u/18722022/LPC122x_LQFP48.zip
(made with EAGLE 6.2, not compatible with EAGLE < 6.0)

Maybe we could have a pinned thread, where useful information and content can be collected? Or maybe the operator of this forum could make use of the unbelievable benefits of subforums? :D

lpcware · ‎06-15-2016

Content originally posted in LPCWare by ex-kayoda on Thu Oct 18 04:23:20 MST 2012
Yes, blame the forum :)

"rtc site:knowledgebase.nxp.com" = About 388 results

"rtc AND 100k site:knowledgebase.nxp.com" = 5 informative results

lpcware · ‎06-15-2016

Content originally posted in LPCWare by Caradhras on Thu Oct 18 04:13:43 MST 2012
Oh thanks for the AppNote. I only used the forum search which gave me zero results :(

lpcware · ‎06-15-2016

Content originally posted in LPCWare by ex-kayoda on Thu Oct 18 04:05:34 MST 2012

Quote:

Question:
The precision of my RTC application will mostly depend on the quality of the used 32k768 crystal?

Yes :)

Quote:

Question:
How did the guys from EA design the caps and resistors used in here?

Google, Forum Search or just reading Freescale Semiconductor Application Notes :eek::confused::p

See #6 of http://knowledgebase.nxp.com/showthread.php?t=3497

lpcware · ‎06-15-2016

Content originally posted in LPCWare by Caradhras on Thu Oct 18 03:57:30 MST 2012
Both :D Im sorry!

Question:
The precision of my RTC application will mostly depend on the quality of the used 32k768 crystal? How did the guys from EA design the caps and resistors used in here?

lpcware · ‎06-15-2016

Content originally posted in LPCWare by ex-kayoda on Thu Oct 18 03:52:51 MST 2012

Quote: Caradhras
Ok, I forgot the evaluation board as a source of information.

But you cannot deny that the UM is in the case of the RTC incomplete at best! It does not state, how to choose the value of the capacitors in in connection to the load capacitance of the 32k768 crystal nor does it say anything about that 100k resistor seen in the evaluation board.

Is this a question or just nagging ?

lpcware · ‎06-15-2016

Content originally posted in LPCWare by Caradhras on Thu Oct 18 03:38:34 MST 2012
Ok, I forgot the evaluation board as a source of information.

But you cannot deny that the UM is in the case of the RTC incomplete at best! It does not state, how to choose the value of the capacitors in in connection to the load capacitance of the 32k768 crystal nor does it say anything about that 100k resistor seen in the evaluation board.

lpcware · ‎06-15-2016

Content originally posted in LPCWare by ex-kayoda on Thu Oct 18 03:15:51 MST 2012

Quote:

The chapter 16 of the UM does not mention the pins and states, that the clock for the RTC is derived from the main clock or from the built in RTC oscillator.

:confused:

Quote:

16.2 Basic configuration
The RTC clock is controlled by the SYSCFG (Table 58) register in the PMU and can be selected from RTC internal oscillator or the main clock.

Quote:

5.3.3 System configuration register
This register controls the clock input to the RTC ...

So RTC circuit in http://www.embeddedartists.com/sites/default/files/docs/schematics/LPCXpressoLPC1200revB.pdf isn't surprising :)