Actions
Forum Thread Details
  • State Not Answered
  • Replies 6 replies
  • Subscribers 61 subscribers
  • Views 1375 views
  • Users 0 members are here
Related

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,

  • 0
    Hi:
     
    “RTC seems stopped and OSCF (Oscillator Failure) flag is set to 1” does not mean that the oscillator stopped working. You should check either it works or not.
     
    Following is the description in CY14B101K datasheet:
     
    “When the device is powered on (VCC goes above VSWITCH), the OSCEN bit is checked for “enabled” status. If the OSCEN bit is enabled and the oscillator is not active within the first 5 ms, the OSCF bit is set to “1”. The system must check for this condition and then write ‘0’ to clear the flag. Note that in addition to setting the OSCF flag bit, the time registers are reset to the “Base Time” (see “Setting the Clock” on page 7), which is the value last written to the time keeping registers. The Control or Calibration registers and the OSCEN bit are not affected by the “oscillator failed” condition.”
    The OSCF is Set to 1 on power up if the oscillator is enabled and not running in the first 5 ms of operation. This indicates that RTC backup power failed and clock value is no longer valid. The user must reset this bit to 0 to clear this condition (Flag). The chip does not clear this flag.
     
    It seems that the clock value is no longer valid, not “RTC seems stopped”, Maybe.
     
    Best wishes,
    Oliver zhang
    Attachments:
    imageCY14B101K1.pdf
  • 0 in reply to Oliver

    Thanks for the answer.

     

    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

     

    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

     

    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.

     

    It is like Oscillations are "pumped" to 0V.

  • 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.

  • 0

    yes, move the supercapacitor away, because the RTC is correct when system is power off. move it to avoid any negative impact.

     

    it is a good choose to replace a good crystal .

     

    best regard!

  • 0 in reply to Oliver

    At Cypress', they are aware of oscillations problems. The reasons are undershoot on some signals and antenna problem.

    They release other ships which avoid undershoot issues and they will release an application note to make a better design.

     

    Thanks for all.