MSP430学习笔记2-ADC12

接《MSP430学习笔记1-I/O端口》

开发版型号：SEED—MSP430F5529A

开发工具   ：CCS 5.4v

以下内容是CCS中ADC12操作的一些简单的demo，现整理如下：

有关MSP430F5529芯片ADC12相关资料，可参考《MSP430x5xx and MSP430x6xx Family User's Guide (Rev. M)——Chapter 28 ADC12_A》

1：demo描述

Description: A single sample is made on A0 with reference to AVcc.

Software sets ADC12SC to start sample and conversion - ADC12SC 

automatically cleared at EOC. ADC12 internal oscillator times sample (16x)

and conversion. In Mainloop MSP430 waits in LPM0 to save power until ADC12

conversion complete, ADC12_ISR will force exit from LPM0 in Mainloop on

reti. If A0 > 0.5*AVcc, P1.0 set, else reset.

参考AVcc电压、以A0定时器作为采样输入信号源的、单通道单次模式采样，当采样信号大于0.5*AVcc时，P1.0置位，否则为0。

代码如下：

 1 #include <msp430.h>
 2 
 3 int main(void)
 4 {
 5   WDTCTL = WDTPW + WDTHOLD;                 // Stop WDT
 6   ADC12CTL0 = ADC12SHT02 + ADC12ON;         // Sampling time, ADC12 on
 7   ADC12CTL1 = ADC12SHP;                     // Use sampling timer
 8   ADC12IE = 0x01;                           // Enable interrupt
 9   ADC12CTL0 |= ADC12ENC;
10   P6SEL |= 0x01;                            // P6.0 ADC option select
11   P1DIR |= 0x01;                            // P1.0 output
12 
13   while (1)
14   {
15     ADC12CTL0 |= ADC12SC;                   // Start sampling/conversion
16 
17     __bis_SR_register(LPM0_bits + GIE);     // LPM0, ADC12_ISR will force exit
18     __no_operation();                       // For debugger
19   }
20 }
21 
22 #pragma vector = ADC12_VECTOR
23 __interrupt void ADC12_ISR(void)
24 {
25   switch(__even_in_range(ADC12IV,34))
26   {
27   case  0: break;                           // Vector  0:  No interrupt
28   case  2: break;                           // Vector  2:  ADC overflow
29   case  4: break;                           // Vector  4:  ADC timing overflow
30   case  6:                                  // Vector  6:  ADC12IFG0
31     if (ADC12MEM0 >= 0x7ff)                 // ADC12MEM = A0 > 0.5AVcc?
32       P1OUT |= BIT0;                        // P1.0 = 1
33     else
34       P1OUT &= ~BIT0;                       // P1.0 = 0
35 
36     __bic_SR_register_on_exit(LPM0_bits);   // Exit active CPU
37   case  8: break;                           // Vector  8:  ADC12IFG1
38   case 10: break;                           // Vector 10:  ADC12IFG2
39   case 12: break;                           // Vector 12:  ADC12IFG3
40   case 14: break;                           // Vector 14:  ADC12IFG4
41   case 16: break;                           // Vector 16:  ADC12IFG5
42   case 18: break;                           // Vector 18:  ADC12IFG6
43   case 20: break;                           // Vector 20:  ADC12IFG7
44   case 22: break;                           // Vector 22:  ADC12IFG8
45   case 24: break;                           // Vector 24:  ADC12IFG9
46   case 26: break;                           // Vector 26:  ADC12IFG10
47   case 28: break;                           // Vector 28:  ADC12IFG11
48   case 30: break;                           // Vector 30:  ADC12IFG12
49   case 32: break;                           // Vector 32:  ADC12IFG13
50   case 34: break;                           // Vector 34:  ADC12IFG14
51   default: break;
52   }
53 }

2：代码分析

1）主函数中代码：

1 ADC12CTL0 = ADC12SHT02 + ADC12ON;         // Sampling time, ADC12 on
2 ADC12CTL1 = ADC12SHP;                     // Use sampling timer
3 ADC12IE = 0x01;                           // Enable interrupt
4 ADC12CTL0 |= ADC12ENC;
5 
6 ADC12CTL0 |= ADC12SC;                   // Start sampling/conversion

参考控制寄存器如下：

 

ADCSHT0x :采样保持定时器0,该四位定义了保存在转换存储寄存器 中转换结果的采样周期；

ADC12ENC：转换允许

ADC12SHP：选择采样定时器A0输出 

ADC12IE：中断允许 (来自中断允许寄存器)

 

2）中断部分代码：

中断寄存向量ADC12IV中的数字（0-36）用来判断中断标志寄存器中相关位是否置位，此时表明转换结果已经装入转换存储寄存器中，具体数字的含义参见下图：

3）

1  if (ADC12MEM0 >= 0x7ff)                 // ADC12MEM = A0 > 0.5AVcc?
2       P1OUT |= BIT0;                        // P1.0 = 1
3     else
4       P1OUT &= ~BIT0;                       // P1.0 = 0

参考电压使用VCC，因为ADC精度为12位（4095），所以0x7FF（2047）就是0.5Vcc的AD值

  

StevenMeng

2013 6.14