MSP430入门-----总算读懂例程中的用调节DCO频率

//******************************************************************************

//  MSP-FET430P140 Demo - Basic Clock, Implement Auto RSEL SW FLL

//

//  Description: Set DCO clock to (Delta)*(4096) using software FLL. DCO clock

//  is output on P5.5 as SMCLK.  DCO clock, which is the selected SMCLK source

//  for timer_A is integrated over LFXT1/8 (4096) until SMCLK is is equal

//  to Delta.  CCR2 captures ACLK.  To use Set_DCO Timer_A must be

//  operating in continous mode.  Watch crystal for ACLK is required for

//  this example.  Delta must be kept in a range that allows possible

//  DCO speeds.  Minimum Delta must ensure that Set_DCO loop

//  can complete within capture interval. Maximum delta can be calculated be

//  f(DCOx7) / 4096.  f(DCOx7) can be found in device specific datasheet.

//  ACLK = LFXT1/8 = 32768/8, MCLK = SMCLK = target DCO

//  //* External watch crystal installed on XIN XOUT is required for ACLK *//

//

//           MSP430F149

//         ---------------

//     /|\|            XIN|-

//      | |               | 32kHz

//      --|RST        XOUT|-

//        |               |

//        |           P5.5|--> SMLCK = target DCO

//        |           P5.6|--> ALCK = 4096

//

//

//  M. Buccini

//  Texas Instruments Inc.

//  Feb 2005

//  Built with IAR Embedded Workbench Version: 3.21A

//******************************************************************************

#include  <msp430x14x.h>

void Set_DCO (void);

void main(void)

{

  WDTCTL = WDTPW + WDTHOLD;                 // Stop WDT

  P5DIR |= 0x60;                            // P5.5,6 output

  P5SEL |= 0x60;                            // P5.5,6 SMCLK, ACLK output

  Set_DCO();                                // Set DCO

  while (1);

}

//------------------------------------------------------------------------------

void Set_DCO (void)                         // Set DCO to selected frequency

//------------------------------------------------------------------------------

{

//#define DELTA 900                           // target DCO = DELTA*(4096) = 3686400

#define DELTA 256                           // target DCO = DELTA*(4096) = 1048576//DCO频率

//#define DELTA 70                            // target DCO = DELTA*(4096) = 286720

  unsigned int Compare, Oldcapture = 0;

  BCSCTL1 |= DIVA_3;                        // ACLK= LFXT1CLK/8

  CCTL2 = CM_1 + CCIS_1 + CAP;              // CAP, ACLK

  TACTL = TASSEL_2 + MC_2 + TACLR;          // SMCLK, cont-mode, clear

  while (1)

  {

    while (!(CCIFG & CCTL2));               // Wait until capture occured

    CCTL2 &= ~CCIFG;                        // Capture occured, clear flag

    Compare = CCR2;                         // Get current captured SMCLK

    Compare = Compare - Oldcapture;         // SMCLK difference

    Oldcapture = CCR2;                      // Save current captured SMCLK

    if (DELTA == Compare) break;            // If equal, leave "while(1)"

    else if (DELTA < Compare)               // DCO is too fast, slow it down

    {

      DCOCTL--;

      if (DCOCTL == 0xFF)

      {

        if (!(BCSCTL1 == (XT2OFF + DIVA_3)))//这儿用实际的数值表示可能更明确点！！//减的极限

        BCSCTL1--;                          // Did DCO roll under?, Sel lower RSEL

      }

    }

    else

    {

      DCOCTL++;

      if (DCOCTL == 0x00)

        {

          if (!(BCSCTL1 == (XT2OFF + DIVA_3 + 0x07)))//加的极限。

          BCSCTL1++;                        // Did DCO roll over? Sel higher RSEL

        }

    }

  }

  CCTL2 = 0;                                // Stop CCR2

  TACTL = 0;                                // Stop Timer_A
}

其中DCOCTL,BCSCTL1的加减需要结合寄存器看。

如果直接写成数值的形式，理解好点。

调节频率，有点类似万用表的电压，先选好档位，再调节。其中BCSCTL1就是档位，而DCOCTL就是说的具体调节。

在每个加减都有溢出情况对于DCOCTL;

BCSCTL1，res0~7,分成八个档位。