Inaccuracy of PIC Microcontroller RTC

[Rikr09]

Reference previous thread:

https://www.edaboard.com/threads/188226/

I had a similar problem with a PIC18F46J11 which lost several seconds every minute. The crystal WAS running at 32768Hz exactly as intended. I don't know if the same applies to your PIC24 device because you haven't told us which one it is, check you are using the crystal oscillator as your timing source. Everything seemed to work properly, including the alarm registers but just a little too slow. The problem was one bit in one register which was making the RTC module derive it's source from the internal slow clock. Unfortunately, it runs at 31KHz not 32.768KHz !! Being so close in frequency it's easy to be misled about the problem.

Brian.

So, you can fix the problem?

 

[Gorgon]

Switch the clock source to the x-tal oscillator, and not the internal RC-oscillator. It's in the quoted text!

 

[Rikr09]

Switch the clock source to the x-tal oscillator, and not the internal RC-oscillator. It's in the quoted text!

Hello Gorgon,

I am using a PIC24FJ128GB204 and i do no have clear how to select exactly the SOSC to my RTC. Just enabling SOSCEN bit?

Thanks for your help!

 

[Gorgon]

You select the RTC clock in the RTCLK bits(10,11), set to 0,0, in the RTCPWC register.

You also need to enable the SOSC as you said.

You can also calibrate the oscillator with values in the RCFGCAL register. see chapter 22.4 in the datasheet https://ww1.microchip.com/downloads/en/DeviceDoc/30005009c.pdf

 

[Rikr09]

You select the RTC clock in the RTCLK bits(10,11), set to 0,0, in the RTCPWC register.

You also need to enable the SOSC as you said.

You can also calibrate the oscillator with values in the RCFGCAL register. see chapter 22.4 in the datasheet https://ww1.microchip.com/downloads/en/DeviceDoc/30005009c.pdf

Hello,

Thanks for your help... I will make some test and then, ill write my results.

Thanks again!