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    Microcontroller is DALI connected but has no external oscillator crystal

    We have some lamps with a DALI dimming facility.
    The PIC micro in the lamp is using its internal oscillator. Do you think this micro will have difficulty “locking in” to the incoming DALI signals?
    Is it "standard practice" to always have an external oscillator?
    Some of the units are not working, and we wonder if this is the cause.

    •   Alt20th May 2017, 00:16

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    Re: Microcontroller is DALI connected but has no external oscillator crystal

    Internal oscillators can often be off by 3%, and vary by temperature.
    However if your DALI device is from a branded manufacturer, surely they would have taken that into consideration.

    Also from what little I know, the initial introduction of a device into a network requires a "commissioning" to be done. I am sure you are aware of this and have done so.

    Were these originally working, and are not not-working ? Or are they new, and maybe from a different manufacturer ?



    •   Alt22nd May 2017, 10:46

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    Re: Microcontroller is DALI connected but has no external oscillator crystal

    We are finding that some units work and some dont



    •   Alt22nd May 2017, 20:15

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    Re: Microcontroller is DALI connected but has no external oscillator crystal

    As you mentioned a PIC device, Microchip have an App Note (http://ww1.microchip.com/downloads/e...tes/01465A.pdf) that uses a PIC16F1947 which, according to the schematic in the app note, is running from the internal oscillator (as no external crystal is shown).
    The App note also shows in text in Figure 7 that the timing required if +/-10%. Even at the widest temperature range fort that chip, the data sheet shows that the HFINTOSC is +/-5% (with the +/-3% mentioned above as the more typical operating temperature range).
    Based on the App Note and the data sheet for the MCU mentioned in the App Note then there is every chance that the design can be reliable. However we don't know the actual MCU used in your case nor the schematic etc. and they will have a major influence on reliability.
    Susan


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