TI中文支持网1、芯片：MSP430F5438A
2、外接晶振：25MHz
3、ADC时钟选择MCLK=25MHz的5分频，即ADC12CLK=5MHz，即0.2us
4、采样保持时间为：16个ADC12CLK cycles，即Tsample=4*0.2*16=12.8us？？？我这样算对吗？？
5、转换时间公式：13 × ADC12DIV × 1/fADC12CLK，即13*5*0.2us=13us
那么我的ad采样一个点转换完的时间是：采样保持时间+转换时间=12.8+13us=25.8us，按照这么算我的采样率才：1/25.8=38.75Ksps？？？
请问我的上述计算方法对吗？
附件1：我的adc初始化代码
void ADC12_Init(void)
{P6SEL |=BIT0 + BIT1 + BIT2;// Enable VeREF+ & A/D channel A0ADC12CTL0 = ADC12ON+ADC12MSC+ADC12SHT0_2; // Turn on ADC12_A, extend sampling time// to avoid overflow of resultsADC12CTL1 = ADC12SSEL_2//时钟选择为：MCLK+ADC12DIV_4//时钟分频为：4+ADC12SHP//采样信号源自采样定时器+ADC12CONSEQ_3;//序列通道多次采样ADC12MCTL0 = ADC12INCH_0;// ref+=AVcc, channel = A0ADC12MCTL1 = ADC12INCH_1;// ref+=AVcc, channel = A1ADC12MCTL2 = ADC12INCH_2+ADC12EOS;// ref+=AVcc, channel = A2, end seq.
}
附件2：我的时钟等代码如下
int main(void)
{WDTCTL = WDTPW + WDTHOLD; // Stop WDT
//##############################################################################//Increase Vcore setting to level3 to support fsystem=25MHzSetVCore(PMMCOREV_1);//Set Vcore level 3 to match higher SVS levelsSetVCore(PMMCOREV_2);//Set Vcore level 3 to match higher SVS levelsSetVCore(PMMCOREV_3);//Set Vcore level 3 to match higher SVS levelsFeed_Dog;//喂外部狗CAT1023，2013-05-06ExCLK_Init();//XT2_Start(XT2DRIVE_3);//设置XT2DRIVE_3可以提高对晶振的驱动能力，2013-04-04Feed_Dog;//喂外部狗CAT1023，2013-05-06DISABLE_SVSL();// SVS Low side is turned offDISABLE_SVML();// Monitor low side is turned offDISABLE_SVMH();// Monitor high side is turned offENABLE_SVSH();// SVS High side is turned onENABLE_SVSH_RESET();SVSH_ENABLED_IN_LPM_FULL_PERF();// Full performance mode,stays on in LPM3// Wait until high side, low side settledwhile(((PMMIFG & SVSMLDLYIFG) == 0)&&((PMMIFG & SVSMHDLYIFG) == 0));// SVSH turns off in LPM3,power-saveCLEAR_PMM_IFGS();// SVS protection set at Level 3/5PMMCTL0_H = 0xA5;SVSMHCTL |= SVSHRVL_3 + SVSMHRRL_5;while((PMMIFG & SVSMHDLYIFG) == 0);// Level reached?PMMCTL0_H = 0x00;CLEAR_PMM_IFGS();
//##############################################################################while(1){;}
}
#pragma vector=UNMI_VECTOR
__interrupt void NMI_ISR(void)
{uint16_t status=0;do{// If it still can't clear the oscillator fault flags after the timeout, trap and wait here.status = Clear_All_Osc_Flags(1000);} while(status != 0);
}
//******************************************************************************
//描述:外部高速时钟初始化，使用xM晶振
//输入:无 输出:无
//******************************************************************************
static void ExCLK_Init(void)
{P5SEL |= 0x0C;// Port select XT2//P7SEL |= 0x03;// Port select XT1UCSCTL6 &= ~XT2OFF; // Enable XT2//下面用SELREF__XT2CLK也可以，2013-03-29UCSCTL3 |= SELREF_2;// FLLref = REFO// Since LFXT1 is not used,// sourcing FLL with LFXT1 can cause// XT1OFFG flag to setUCSCTL4 |= SELA_2; // ACLK=REFO,SMCLK=DCO,MCLK=DCOUCSCTL6 |= XT2DRIVE_3;// Decrease XT2 Drive according to expected frequency//+ XT2BYPASS;//XT2 sourced from external pin// Loop until XT1,XT2 & DCO stabilizesdo{UCSCTL7 &= ~(XT2OFFG + XT1LFOFFG + XT1HFOFFG + DCOFFG);// Clear XT2,XT1,DCO fault flagsSFRIFG1 &= ~OFIFG;// Clear fault flags}while(SFRIFG1&OFIFG);// Test oscillator fault flagUCSCTL4 |= SELA__XT2CLK + SELS__XT2CLK + SELM__XT2CLK;//时钟选择//UCSCTL5 |= DIVA_1;//ACLK=XT2CLK/2,SMCLK=XT2CLK,MCLK=XT2CLK,2013-04-03
}
kqian0327：
你好，
我认为你理解的完全正确，请问你的问题是？觉得采样率太低了？
xtaens：
回复 kqian0327:
我的问题就是我的理解对吗？？？
如果对的话，这样的话这个采样率也太太低了吧
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现在我用5438A的ADC每隔45us采样一个光电传感器的信号，现在发现有时AD值采样不上，就是开始能采集到信号，中间丢了一段
后面就又有了。不知这个现象怎么解释呢
