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Using DCO Library for Frequency Locked Loop on MCLK using ACLK

K.Kerem Oktem
Prodigy 80 points
Other Parts Discussed in Thread: MSP430F4618

Dear All,

I am confused with some issue on my circuit that is using MSP430F4618 micrcontroller.

I am using a 32kHz crystal for the ACLK. I want to gererate a FLLed clock for the MCLK. For this i want to use the DCO library. However i am confused.

The problem is:

For FLL, the compare channel is used in the TimerA. The clock for the Timer is fed with the DCO and the compare channel is chosen for the ACLK(32kHz).

It is said in the datasheet that for 4618 CCI2B is internally connected to the ACLK. But also in the datasheet pin2.3 can be configured for CCI2A/CCI2B.

So how can i know if the CCI2B is connected to pin2.3 or internally to ACLK.

Kind Regarsds

Kerem OKTEM

  • 0
    Guru 227245 points

    I think you're mixing lots of things together which are unrelated.

    1) the 4x family has a hardware FLL which uses XT1 as reference. XT1 is also connected with ACLK, but ACLK is not related to FLL.
    2) the DCO library doesn't use the hardware FLL but implements one in software by counting DCO clock ticks with the timer and triggering a captur einterrupt in ACLK. Effectively the same the hardware FLL does, but wasting a timer and lots of CPU cycles.
    3) Timer A CCR2 unit has (besides VCC and VSS) two possible trigger sources for the capture interrupt. TA0CCI2A and TA0CCI2B. The first one is conencted to the external TA2 signal, available on pin 79 (P2.0)and the other is internally connected to ACLK.
    4) Pin 76 (P2.3) carries the external TB2 signal, which is available to Timer B CCR2 unit on both selections, TB0CCI2A and TB0CCI2B.

  • 0 in reply to Jens-Michael Gross
    Prodigy 80 points

    Dear Mr. Gross,

    You are correct that my question is a little odd.

    I know that the 4 series have  FLL already built inside. But i just gave that series as an example.

    My basic question is for general MSP430 MCU.

    Is this what you are saying: For TimerA CCI2A can be connected to pin2.0  and /CCI2B is already connected to ACLK.

    And for timerB the CCI2A and CCI2B can be connected pin2.3 and not really connected to ACLK.

    I think you have already cleared up my mind. Thank you very much.

    Kind Regards

  • 0 in reply to K.Kerem Oktem
    Guru 227245 points

    K.Kerem Oktem said:
    My basic question is for general MSP430 MCU.

    Most clock system dependent questions are family specific. 1x, 2x, 4x , 5/6x and FR5x family all have a widely different clock system. The basic ideas (DCO, ACLK, MCLK, SMCLK) are the same, but implementation, features, registers are completely different. And the FR5x series' DCO is a completely different breed.

    K.Kerem Oktem said:
    Is this what you are saying: For TimerA CCI2A can be connected to pin2.0  and /CCI2B is already connected to ACLK.
    And for timerB the CCI2A and CCI2B can be connected pin2.3 and not really connected to ACLK.


    Yes - for this specific device.
    Generally, each Timer CCR unit has two possible inputs for capture mode, but how these two inputs are connected (internal signal, external pin, twice the same pin or two different pins), depends on each individual device. You must check the device datasheet (the peripherals/TimerA or TimerB section) for a table of what is connected where.

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