MSP430F149的ADC12应用

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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。

参考框图：

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

主要参数进行配置

• 设置工作方式：四种方式选一： sing;sequence;re-sing;re-sequence;
• 设置转换时间：SHTx
• 设置触发源：ADC12SC;MSC;TimerA;TimerB
• 设置通道：外部通道;内部Temperature sensor
• 设置参考电压：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）。

ADC12模数转换是在SHI的上升沿初始化的。
SHI信号有四个来源–参考ADC12CTL1寄存器说明：

• 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

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• SHT1x Bits:15-12; Sample-and-hold time.

  These bits define the number of ADC12CLK cycles in the sampling period for registers ADC12MEM8 to ADC12MEM15.

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• SHT0x Bits: 8-11; Sample-and-hold time.

  These bits define the number of ADC12CLK cycles in the sampling period for registers ADC12MEM0 to ADC12MEM7.

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• 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.

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• ADC12ON : Bit 4; ADC12 on
  
  • 0 : ADC12 off
  • 1 : ADC12 on

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• ENC: ENC Bit 1; Enable conversion
  
  • 0 : ADC12 disabled
  • 1 : ADC12 enabled

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• 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

2、ADC12CTL1

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• CSTARTADDx: Bit 15-12;

  Conversion start address. These bits select which ADC12 conversion-memory register is used for a single conversion or for the first conversion in a sequence. The value of CSTARTADDx is 0 to 0Fh, corresponding to ADC12MEM0 to ADC12MEM15.

• SHSx: Bits 11-10; Sample-and-hold source select

  • 00 : ADC12SC bit
  • 01 : Timer_A.OUT1
  • 10 : Timer_B.OUT0
  • 11 : Timer_B.OUT1

• 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.

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• ISSH: Bit 8; Invert signal sample-and-hold
  
  • 0 The sample-input signal is not inverted.
  • 1 The sample-input signal is inverted.

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• ADC12DIVx: Bits 7-5; ADC12 clock divider

  • 000 /1
  • 001 /2
  • 010 /3
  • 011 /4
  • 100 /5
  • 101 /6
  • 110 /7
  • 111 /8

• ADC12 SSELx: Bits 4-3; ADC12 clock source select.

  • 00 ADC12OSC
  • 01 ACLK
  • 10 MCLK
  • 11 SMCLK

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• 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

• ADC12 BUSY: Bit 0; ADC12 busy. This bit indicates an active sample or conversion operation.

  • 0 No operation is active.
  • 1 A sequence, sample, or conversion is active.

3、ADC12IE

ADC12 Interrupt Enable Register

- 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

ADC12 Interrupt Flag Register

• 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

ADC12 Conversion Memory Control Registers

- EOS: Bit 7; End of sequence.

Indicates the last conversion in a sequence.
- 0 Not end of sequence
- 1 End of sequence

• 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

6、ADC12MEMx

ADC12 Conversion Memory Registers

Conversion Results: Bit 15-0;

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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? - 等待设置完成

  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

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