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RTC (Real Time clock) Cypress oscillator fails (oscf flag = 1), what happens ?

mmtsuchi

Hi,

 

On a custom bord, I have a RTC Cypress CY14B101k wich is a nvRAM, with Real Time Clock Calendar, Alarm Clock and Watchdog.

This board uses a superCapacity (not battery) for this "RTC".

 

When the board is OFF, RTC is running quite well : the time seems correct.

 

The problem is when the board is ON, the RTC seems stopped and OSCF (Oscillator Failure) flag is set to 1.

My question is : What are the reasons that causes oscillator stop ?

 

I don't use Watchdog, alarm, interrupt.

Writing a 0 to OSCEN_n causes OSCF=0 (good) but 6 seconds later OSCF=1 and the time is not running.

 

Best regards,

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  • 0
    I "scoped" the quartz signals. I may introduce impedance with the oscilloscope.
    When the RTC chip is on CAPacitor, I can see sinusoïdal waveform with an offset. VX1= 0.4Vac + 0.6Vdc
    ÞThat is right! When the RTC chip is on capacitor, the /OSCEN bit should be set to 1 to turn off the oscillator to extend the battery life.
    When the RTC chip is not sollicited (Address bus and data bus not changed during 10  seconds), I can see high sinusoïdal waveform VX1= 1.4Vac + 0.7Vdc
    ÞIt seems that the oscillator is working, because that you can see high sine waveform on VX1 pin. I think if you can see vx1=1.4v ac, the data and address buses should be changed definitely.
    This RTC chip shares its address bus and data bus with SRAM and FLash.
    Tests of address bus and data bus (verify if one is "stuck") are OK.
    On a Application Note form Cypress, it is reported that undershoot may stop Oscillator. I put Schottky diode on critical signals to limit undershoot.But no changes.
    ÞWhere you put the schottky diode? On an app note from Cypress, the undershoot less than -0.5v may stop oscillator, but there is an offset on vx1 pin, so the minimum value of sine waveform is zero.
    You can debug the trouble step by step:
    Move the capacitor away, then power on the system, set /OSCEN bit=0 to enable oscillator. Use scope to test the vx1 pin after 5-10s. Pls monitor the OSCF bit continuous, if the oscillator is stopped, OSCF bit will be set to 1, and you should write a zero to clear the flag.
    Do not care the time is correct or not.
    Best wishes,
    Oliver zhang
  • 0 in reply to Oliver

    Hi,

     

    I put SMD Schottky Diodes on DO, A[3..0].

    It is better but not enough : oscillations can be observed but they are attenuated slowly.

     

    "move the capacitor away" Do you mean the supercapacitor ?

     

    I also wrote a thread on Cypress site. They answer well and quickly. do not see any concurrence :-)

    My problem is still here.

     

    I may suspect my quartz because of marketing information.

    Best regards.

Reply
  • 0 in reply to Oliver

    Hi,

     

    I put SMD Schottky Diodes on DO, A[3..0].

    It is better but not enough : oscillations can be observed but they are attenuated slowly.

     

    "move the capacitor away" Do you mean the supercapacitor ?

     

    I also wrote a thread on Cypress site. They answer well and quickly. do not see any concurrence :-)

    My problem is still here.

     

    I may suspect my quartz because of marketing information.

    Best regards.

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