RTC clock on LPC4370

[lpcware]

Content originally posted in LPCWare by JohnR on Thu Oct 02 10:07:55 MST 2014
Hi,

I am considering implementing a RTC in a system that uses a LPC4370, the 100 pin version.

Looking through the lpcware forums there seem to have been a number of problems with on-chip RTCs.

Should I implement the RTC with the internal clock or use an external one?

If I use the internal clock, what are the recommended crystals and associated capacitors?

Thanks in advance for any help,

JohnR.

[lpcware]

Content originally posted in LPCWare by JohnR on Mon Oct 06 04:11:45 MST 2014
Hi Bavarian,

Thanks for the reply.

JohnR

[lpcware]

Content originally posted in LPCWare by bavarian on Mon Oct 06 02:44:04 MST 2014
In general I don't agree to the statement that there are "number of problems with the on-chip RTC".

The only nasty problem I know is that it takes considerably long to initialize the RTC. This could take up to 3 seconds. This is due to the implementation of this RTC block in the 3-core system (many different timing domains) and due to the strong focus on low power implementation.
Read access is much faster, there is no such delay.
Also the granularity of 1 second differentiates this RTC from others, you can't to do something in the milliseconds range.
The RTC requires an external 32.768 crystal, you can't derive this frequency from another on-chip clock source.
For the capacitors please look into some the examples for the LPC4300 (boards from Keil, Hitex, NGX, etc).

Regards,
NXP Support Team