MSP430F149的ADC12模块

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MSP430F149的ADC12模块 [复制链接]

1 概述

  MSP430F149的ADC12为SAR型12位AD,共有16路输入通道，其中8路独立的外部输入通道，2路接外部Vref+,Vref-，3路内部通道可分别测内部温度传感器、AVCC、和外部参考源。

    P6口第二功能为AD输入端。MSP430F149的10、11分别接外部电压参考源正负极，7脚可将内部电压参考源输出。

    ADC12共有18个中断源，公用一个中断向量ADC12_VECTOR。

AD的参考源可选择内部电压参考源或外部电压参考源。内部电压参考源有1.5V,2.5V可选，使用时向ADC12CTL0写入REFON+ REF2_5V就打开了2.5V。外部电压参考源由REF+接入。上电时若不设置参考源，则参考源为系统供电电压3.3V。

2 使用方法概述

2.1程序架构

中断方式

    1、设置  ADC12工作模式，启动转换，开全局中断，等待中断

    2、写中断处理函数

查询方式

    设置ADC12工作模式，启动转换，查询中断标志ADC12IFG

    while (!(0x01 & ADC12IFG));转换完毕读取采样值，系统自动清除中断标志

2.2 使用概述

主要参数配置

设置工作方式：sing\\sequence\\re-sing\\re-sequencd;

设置转换时间：SHTX

设置触发方式：ADC12SC\\MSC\\TimerA\\ TimerB

设置通道：外部通道\\内部Temperature sensor

设置参考源：系统电压\\内部参考源\\外部参考源

其他细节配置

     一般要配置采样转换模式为脉冲（SHP）,打开ADC12(ADC12ON),使能ADC12转换(ENC)，使能中断（如果采取中断模式），触发转换（若采用ADC12SC触发）。

解释

ADC12模数转换是在SHI的上升沿初始化的。SHI信号有四个来源： The ADC12SC bit；The Timer_A Output Unit 1； The Timer_B Output Unit 0； The Timer_B Output Unit 1。故单次采样时只需要每次设置ADC12CTL0 |= ADC12SC就采样一次；重复采样时，如Rep-sing，设置ADC12CTL1 = SHS_1 +CONSEQ_2就选择了Rep-sing模式，每次采样通过定时器A触发。

3 相关寄存器

1、ADC12CTL0

SHT1x Bits

Sample-and-hold time. These bits define the number of ADC12CLK cycles in

the sampling period for registers ADC12MEM8 to ADC12MEM15.

SHT0x Bits

Sample-and-hold time. These bits define the number of ADC12CLK cycles in

the sampling period for registers ADC12MEM0 to ADC12MEM7.

ADC12ON

0 ADC12 off

1 ADC12 on

ENC

ENC Bit 1 Enable conversion

0 ADC12 disabled

1 ADC12 enabled

ADC12SC Bit 0 Start conversion. Software-controlled sample-and-conversion start.

ADC12SC and ENC may be set together with one instruction. ADC12SC is

reset automatically.

0 No sample-and-conversion-start

1 Start sample-and-conversion

MSC Bit 7 Multiple sample and conversion. Valid only for sequence or repeated modes.

0 The sampling timer requires a rising edge of the SHI signal to trigger

each sample-and-conversion.

1 The first rising edge of the SHI signal triggers the sampling timer, but

further sample-and-conversions are performed automatically as soon

as the prior conversion is completed.

2、ADC12CTL1

SHP

SHP Bit 9 Sample-and-hold pulse-mode select. This bit selects the source of the

sampling signal (SAMPCON) to be either the output of the sampling timer or

the sample-input signal directly.

0 SAMPCON signal is sourced from the sample-input signal.

1 SAMPCON signal is sourced from the sampling timer.

SHSx Bits

11-10

Sample-and-hold source select

00 ADC12SC bit

01 Timer_A.OUT1

10 Timer_B.OUT0

11 Timer_B.OUT1

CONSEQx Bits

2-1

Conversion sequence mode select

00 Single-channel, single-conversion

01 Sequence-of-channels

10 Repeat-single-channel

11 Repeat-sequence-of-channels

3、ADC12IE

ADC12IEx Bits

15-0

Interrupt enable. These bits enable or disable the interrupt request for the ADC12IFGx bits.

0 Interrupt disabled

1 Interrupt enabled

4、ADC12IFG

ADC12IFGx Bits

15-0

ADC12MEMx Interrupt flag. These bits are set when corresponding

ADC12MEMx is loaded with a conversion result. The ADC12IFGx bits are

reset if the corresponding ADC12MEMx is accessed, or may be reset with

software.

0 No interrupt pending

1 Interrupt pending

5、ADC12MCTLX

SREFx Bits

6-4

Select reference

000 VR+ = AVCC and VR− = AVSS

001 VR+ = VREF+ and VR− = AVSS

010 VR+ = VeREF+ and VR− = AVSS

011 VR+ = VeREF+ and VR− = AVSS

100 VR+ = AVCC and VR− = VREF−/ VeREF−

101 VR+ = VREF+ and VR− = VREF−/ VeREF−

110 VR+ = VeREF+ and VR− = VREF−/ VeREF−

111 VR+ = VeREF+ and VR− = VREF−/ VeREF−

INCHx Bits

3-0

Input channel select

0000 A0

0001 A1

0010 A2

0011 A3

0100 A4

0101 A5

0110 A6

0111 A7

1000 VeREF+

1001 VREF−/VeREF−

1010 Temperature sensor

1011 (AVCC – AVSS) / 2

1100 (AVCC – AVSS) / 2

1101 (AVCC – AVSS) / 2

1110 (AVCC – AVSS) / 2

1111 (AVCC – AVSS) / 2

EOS Bit 7 End of sequence. Indicates the last conversion in a sequence.

0 Not end of sequence

1 End of sequence

4实例

4.1 single采样，参考电源为系统电源

1.设置ADC12CTL0，使ADC12通道0采样保持时间为16 ADC12CLK(SHT0_2),开启ADC12模块（ADC12ON）；

2.设置ADC12CTL1，选择采样保持脉冲模式即SAMPCON为采样定时器（SHP）

3.设置ADC12IE,是通道0中断使能（0x01）;

4.设置ADC12CTL0,使能AD转换（ENC）

5.设置模拟信号输入IO口P60

7.设置ADC12CTL0，开启AD转换(ADC12SC),等待中断

8.中断中读取通道0转换值ADC12MEM0

  ADC12CTL0 = SHT0_2 + ADC12ON;             // Set sampling time, turn on ADC12

  ADC12CTL1 = SHP;                          // Use sampling timer

  ADC12IE = 0x01;                           // Enable interrupt

  ADC12CTL0 |= ENC;                         // Conversion enabled

  P6SEL |= 0x01;                            // P6.0 ADC option select

  P2DIR |= 0x01;

ADC12CTL0 |= ADC12SC;

#pragma vector=ADC12_VECTOR

__interrupt void ADC12_ISR (void)

{

    if (ADC12MEM0 < 0x7FF)

      P2OUT = 0;                       // Clear P1.0 LED off

    else

      P2OUT = 0XFF;                        // Set P1.0 LED on

    __low_power_mode_off_on_exit();

    // 与上面等价_BIC_SR_IRQ(CPUOFF);                    // Clear CPUOFF bit from 0(SR)

}

4.2 single采样参考源为2.5V

在ADC12CTL0中设置参考源

在ADC12MCTL0中为通道0选择参考源

  ADC12CTL0 = ADC12ON+SHT0_2+REFON+REF2_5V; // Turn on and set up ADC12

  ADC12CTL1 = SHP;                          // Use sampling timer

  ADC12MCTL0 = SREF_1;                      // Vr+=Vref+

  for ( i=0; i<0x3600; i++);                  // Delay for reference start-up

  ADC12CTL0 |= ENC;  

  while (1)

  {

    ADC12CTL0 |= ADC12SC;                   // Start conversion

    while ((ADC12IFG & BIT0)==0);

    _NOP();                                 // SET BREAKPOINT HERE

  }

4.3 Repeat-single采样,模拟输入为内部Temperature sensor

设置ADC12CTL1，采样保持源为定时器A,脉冲保持模式，Repeat-single模式

  ADC12CTL1 = SHS_1 + SHP + CONSEQ_2;       // TA trig., rpt conv.

设置ADC12MCTL0，通道0参考源为内部REF,模拟输入通道0选择为Temperature sensor

  ADC12MCTL0 = SREF_1 + INCH_10;            // Channel A10, Vref+

  ADC12IE = 0x01;                           // Enable ADC12IFG.0

  ADC12CTL0 = SHT0_8 + REF2_5V + REFON + ADC12ON + ENC; // Config ADC12

  TACCTL1 = OUTMOD_4;                       // Toggle on EQU1 (TAR = 0)

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

  while (!(0x01 & ADC12IFG));               // First conversion?

  FirstADCVal = ADC12MEM0;                  // Read out 1st ADC value

  _BIS_SR(LPM0_bits + GIE);                 // Enter LPM0 w/ interrupt

#pragma vector=ADC12_VECTOR

__interrupt void ADC12ISR (void)

{

  if (ADC12MEM0 <= FirstADCVal + ADCDeltaOn)

      P1OUT &= ~0x01;                       // LED off

  else P1OUT |= 0x01;                       // LED on

}

摄氏温度和温度传感器电压转换关系：0摄氏度对应986mv，1摄氏度温差对应1.97mv温差

//  oF = ((x/4096)*1500mV)-923mV)*1/1.97mV = x*761/4096 - 468

//  IntDegF = (ADC12MEM0 - 2519)* 761/4096

    IntDegF = (temp - 2519) * 761;

    IntDegF = IntDegF / 4096;

//  oC = ((x/4096)*1500mV)-986mV)*1/3.55mV = x*423/4096 - 278

//  IntDegC = (ADC12MEM0 - 2692)* 423/4096

    IntDegC = (temp - 2692) * 423;

    IntDegC = IntDegC / 4096;

4.4 Repeat-sequence mode

Sequence模式时可以设置多个采样通道。在最后一个通道加上EOS就表明的采样通道结束位置。中断允许只需要设置最后一个通道。

为了采样速率尽可能快，可设置MSC,此时当SHI上升沿触发第一次采样后，后面的采样在上一次采样结束后自动进行。

  ADC12CTL0 = ADC12ON+MSC+SHT0_8;           // Turn on ADC12, extend sampling time

                                            // to avoid overflow of results

  ADC12CTL1 = SHP+CONSEQ_3;                 // Use sampling timer, repeated sequence

  ADC12MCTL0 = INCH_0;                      // ref+=AVcc, channel = A0

  ADC12MCTL1 = INCH_1;                      // ref+=AVcc, channel = A1

  ADC12MCTL2 = INCH_2;                      // ref+=AVcc, channel = A2

  ADC12MCTL3 = INCH_3+EOS;                  // ref+=AVcc, channel = A3, end seq.

  ADC12IE = 0x08;                           // Enable ADC12IFG.3

  ADC12CTL0 |= ENC;                         // Enable conversions

  ADC12CTL0 |= ADC12SC;                     // Start conversion

  _BIS_SR(LPM0_bits + GIE);                 // Enter LPM0, Enable interrupts

#pragma vector=ADC12_VECTOR

__interrupt void ADC12ISR (void)

{

  static unsigned int index = 0;

  A0results[index] = ADC12MEM0;             // Move A0 results, IFG is cleared

  A1results[index] = ADC12MEM1;             // Move A1 results, IFG is cleared

  A2results[index] = ADC12MEM2;             // Move A2 results, IFG is cleared

  A3results[index] = ADC12MEM3;             // Move A3 results, IFG is cleared

  index = (index+1)%Num_of_Results;         // Increment results index, modulo; Set Breakpoint here

}