RTC failure [RA4M1]

I have a RA4M1 on which the RTC is not incrementing. The waveforms on the crystal are identical to one that does work. All the other functions of the processor also seem to work.

I know that anything is possible, but it is it at all likely that i have a processor where everything works except the RTC? Or should i continue looking for a hardware fault?

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  • Hello Ian,

    Thanks for your response!

    Could you please provide to us some sample code of the register settings you have done by following the procedure shown in the previous answer?



  • I’m just getting back to this project. . . 
    I found what the problem was.I had misinterpreted the instructions about the software reset. I assumed that it cleared the time registers which I didn’t want to do, so I omitted that step, and that fixed the (only) one which wasn’t working.

    I then found two more that didn’t work because the 32768Hz crystal oscillator wasn’t oscillating, and the instructions in the manual are just plain wrong.

    Rf is nothing to do with the resonator, Rf is required to bias the amplifier. Whether it is needed or not depends only on the amplifier.

    Nor is Rd anything to do with damping, it adds the extra phase shift. A crystal has a phase shift that is asymptotic to 180°, but the amplifier needs 180° phase shift to oscillate, which the crystal on its own cannot provide. Normally the amplifier output resistance and the first capacitor provide the extra phase shift, but if that is insufficient, the Rd is required.

    Most other micros I have used include Rf, though devices like 74HC4060 which also employ Pierce oscillators don’t. But the manual doesn’t specify whether an external Rf is required or not, giving me some nonsense that it is dependent on the crystal.

    Crystals don’t have any significant parallel resistance.

  • I’m still having problems with the RTC.On several units out in the field it appears to change at random, or stop altogether.The RA4M1 has replaced a NXP LPC1517 and an external DS1338,  and that never had any problems.

    Going back to the Pierce oscillator. The on-chip amplifier must have an internal Rf and Rd, if I know the target values, then I need to know the internal values in order to calculate what external values I need to add.

    what should be the voltage (peak to peak, and average DC level) on the IN and OUT pins? If I have made an oscillator out of a 74HCU04, the average DC level would be half the supply voltage, but I note that it isn’t on the RA4M1. That could be because the oscillator is running from a lower voltage supply than Vcc. Could you please clarify.

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