msp430x24x_fll_01.s43

来自「步进电机驱动程序msp430f247单片机」· S43 代码 · 共 96 行

;******************************************************************************
;  MSP430x24x Demo - Basic Clock, Implement Auto RSEL SW FLL
;
;  Description: Set DCO clock to (Delta)*(4096) using software FLL. DCO clock
;  is output on P1.4 as SMCLK.  DCO clock, which is the selected SMCLK source
;  for timer_A is integrated over LFXT1/8 (4096) until SMCLK 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 by 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 *//
;
;           MSP430F49
;         ---------------
;     /|\|            XIN|-
;      | |               | 32kHz
;      --|RST        XOUT|-
;        |               |
;        |           P1.4|--> SMLCK = target DCO
;
;  B. Nisargax
;  Texas Instruments Inc.
;  September 2007
;  Built with IAR Embedded Workbench Version: 3.42A
;******************************************************************************
#include "msp430x24x.h"
;-------------------------------------------------------------------------------
Delta       EQU     2930   ; target DCO = DELTA*(4096) = 12MHz
;Delta       EQU     900    ; target DCO = Delta*(4096) = 3686400
;Delta       EQU     600    ; target DCO = Delta*(4096) = 2457600
;Delta       EQU     250    ; target DCO = Delta*(4096) = 1024000
;Delta       EQU     078    ; target DCO = Delta*(4096) =  319488
;Delta       EQU     070    ; target DCO = Delta*(4096) =  286720
;-------------------------------------------------------------------------------
            RSEG    CSTACK                  ; Define stack segment
;-------------------------------------------------------------------------------
            RSEG    CODE                    ; Assemble to Flash memory
;-------------------------------------------------------------------------------
RESET       mov.w   #SFE(CSTACK),SP         ; Initialize stackpointer
StopWDT     mov.w   #WDTPW+WDTHOLD,&WDTCTL  ; Stop WDT
            push.w  #0ffffh                 ; LFXT1 startup delay
OscDelay    dec.w   0(SP)                   ; Do calc on the stack
            jnz     OscDelay                ;
            incd.w  SP                      ; Correct SP
SetupP1     bis.b   #010h,&P1DIR            ; P1.4 output
            bis.b   #010h,&P1SEL            ; P1.4 SMCLK output
            call    #Set_DCO                ; Set DCO clock
                                            ;
Mainloop    bis.w   #CPUOFF+GIE,SR          ; CPU is not required
            nop                             ; Required only for debugger
                                            ;
;-------------------------------------------------------------------------------
Set_DCO;    Subroutine: Sets DCO to selected frequency based on Delta.
;           R13, R14, and R15 are used, ACLK= 32768/8 Timer_A clocked by DCOCLK
;-------------------------------------------------------------------------------
            bis.b   #DIVA_3,&BCSCTL1        ; ACLK = LFXT1CLK/8
            clr.w   R15                     ;
Setup_CC2   mov.w   #CM_1+CCIS_1+CAP,&TACCTL2  ; CAP, ACLK
Setup_TA    mov.w   #TASSEL_2+MC_2,&TACTL   ; SMCLK, Continous Mode
Test_DCO    bit.w   #CCIFG,&TACCTL2         ; Test capture flag
            jz      Test_DCO                ;
            bic.w   #CCIFG,&TACCTL2         ; Clear capture flag
                                            ;
AdjDCO      mov.w   &TACCR2,R14             ; R14 = captured SMCLK
            sub.w   R15,R14                 ; R14 = capture difference
            mov.w   &TACCR2,R15             ; R15 = captured SMCLK
            cmp.w   #Delta,R14              ; Delta = SMCLK/(32768/4)
            jlo     IncDCO                  ;
            jeq     DoneDCO                 ;
DecDCO      dec.b   &DCOCTL                 ; Slow DCO with DCO and MOD
            jc      Test_DCO                ; Slower?
            bit.b   #00fh,&BCSCTL1          ; Can RSELx be decremented
            jnc     Test_DCO                ; No
            dec.b   &BCSCTL1                ; Decrement RSEL.x
            jmp     Test_DCO                ;
IncDCO      inc.b   &DCOCTL                 ; Speed DCO with DCO and MOD
            jnc     Test_DCO                ; Faster?
            mov.b   &BCSCTL1,R13            ; Can RSEL.x be increased?
            and.b   #00fh,R13               ;
            cmp.b   #00fh,R13               ;
            jz      Test_DCO                ; No
            inc.b   &BCSCTL1                ; Increment RSEL.x
            jmp     Test_DCO                ;
DoneDCO     clr.w   &TACCTL2                ; Stop TACCR2
            clr.w   &TACTL                  ; Stop Timer_A
            ret                             ; Return from subroutine
                                            ;
;-------------------------------------------------------------------------------
            COMMON  INTVEC                  ; Interrupt Vectors
;-------------------------------------------------------------------------------
            ORG     RESET_VECTOR            ; POR, ext. Reset
            DW      RESET
            END