Internal RTC goes forward 3 seconds every minute

[lpcware]

Content originally posted in LPCWare by askar on Sat Dec 20 00:03:43 MST 2014
Hi, everybody

Could someone kindly help me about using Internal RTC in Lpc4357?
i am using a board based on Keil project and using Internal Rtc with 32khz external crystal.
when i initialize the Rtc and set it with Date and Time according to am accurate system, i
saw that its time goes forward 3 seconds after every minute!!!.
I think there must be malfunction in somewhere maybe in my board or software.
and it will be very strange if the problem  is from Lpc4357.
The Calibration is disabled in Rtc. I compared the number of SysTicks between each minute
and for 10 minutes in successive, there were numbers such as 61000,60500,59000,58000,57800,57400,57200,56800,58000,
57700.
any help is appreciated in advance.

Best Regards,

[lpcware]

Content originally posted in LPCWare by askar on Sat Dec 27 05:31:52 MST 2014

Hi, MikeSimmonds and embd02161991

And thanks for your helps,
After many testings I Found out that one of LCD data lines has interference with RTC crystal input lines.
I disabled the LCD data that was Green_4, then RTC was operating well.

Best Regards,

[lpcware]

Content originally posted in LPCWare by embd02161991 on Sun Dec 21 16:18:35 MST 2014
Hi,

Please use the example from LPCOpen package in the following link :

http://www.lpcware.com/content/nxpfile/lpcopen-software-development-platform-lpc43xx-packages

Please choose correct load capacitors for the RTC. The load capacitors for the RTC can be found in the datasheet and also you can refer to the schematics of any of the evaluation boards.

http://www.lpcware.com/content/nxpfile/lpc435x3x2x1x-data-sheet-flash-based-parts

Thanks,
NXP Technical Support

[lpcware]

Content originally posted in LPCWare by MikeSimmonds on Sun Dec 21 04:59:48 MST 2014
I am not a harware person, but maybe you have the wrong value capacitors for your crystal.

Is it possible to set the 'clock out pin' to the RTC crystal [I can do this on a 1778, but have not used 43XX]
Then you can measure with an oscilliscope to verify the 32KHz crystal input.

Yes you can; look at section "12.6.14 BASE_OUT_CLK register" in the UM10503

Rgds, Mike