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External Crystal and DCO at the same time???

Stan Ross
Prodigy 160 points

Other Parts Discussed in Thread: MSP430F2618

I have a MSP430F2618 project with many PCBs in the field. I'm using the DCO running at 1mhz as the only clock source. Everything is working well except I'm getting an inordinate number of over run errors on the internal UART (UCA1xxx). Looking at the programming guide I see that running at 1mhz and using 115k baud results in some high error rates. Turns out I have an un-used 16mhz crystal on every board tied to Xin / Xout (Pins 8 & 9). I would like to use this crystal to drive ACLK and then use ACLK as my clock just for the UART. The question is - can I use the external crystal just for ACLK and leave the DCO running MCLK and SMCLK?

  • 0
    TI__Intellectual 1550 points

    Stan Ross said:

    can I use the external crystal just for ACLK and leave the DCO running MCLK and SMCLK?

    You can choose the clock source of ACLK on basic clock system+. You may check page 278 of MSP430x2xx Family User's Guide. The following information is from the guide.

    Three clock signals are available from the basic clock module+:

    • ACLK: Auxiliary clock. ACLK is software selectable as LFXT1CLK or VLOCLK. ACLK is divided by 1,2, 4, or 8. ACLK is software selectable for individual peripheral modules.

    • MCLK: Master clock. MCLK is software selectable as LFXT1CLK, VLOCLK, XT2CLK (if available on-chip), or DCOCLK. MCLK is divided by 1, 2, 4, or 8. MCLK is used by the CPU and system.

    • SMCLK: Sub-main clock. SMCLK is software selectable as LFXT1CLK, VLOCLK, XT2CLK (if available on-chip), or DCOCLK. SMCLK is divided by 1, 2, 4, or 8. SMCLK is software selectable for individual peripheral modules.

    Richard Park

     

  • 0
    Guru 58965 points

    1 mHz is a rather slow. I hope you mean 1 MHz.

    Even at MCLK = 1 MHz, you may get data overrun error when serving a 115k UART.

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