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STM32用作编码器接口的原理.html
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<h1>STM32用作编码器接口的原理</h1>
<h4>2011-10-25，整理于2014-09-25 / xiahouzuoxin</h4>
<h4>Tags: ARM</h4>
转载请注明出处: <a href="http://xiahouzuoxin.github.io/notes/">http://xiahouzuoxin.github.io/notes/</a>
<div id="TOC">
<ul>
<li><a href="#关于定时器实现编码器计数的两点说明">关于定时器实现编码器计数的两点说明</a></li>
<li><a href="#实例代码调试通过">实例代码（调试通过）</a></li>
</ul>
</div>
<!---title:STM32用作编码器接口的原理-->
<!---keywords:ARM-->
<!---date:2011-10-25，整理于2014-09-25-->
<p>这是一篇旧文，早在上大二的时候，在地下室（当时实验室在防空地下室）顺手在word上写的，当时STM32正刚刚开始蓬勃发展，如今时隔3年，整理到这里！</p>
<h2 id="关于定时器实现编码器计数的两点说明">关于定时器实现编码器计数的两点说明</h2>
<ol style="list-style-type: decimal">
<li><p>外部编码器为定时器提供带有方向的时钟，如下图1右上角。通用定时器总共四种时钟提供方式，现在使用的即是TI1F和TI2F的组合时钟方式。</p>
<div class="figure">
<img src="../images/STM32用作编码器接口的原理/img1.png" alt="img1" /><p class="caption">img1</p>
</div></li>
<li><p>TI1、TI2作为编码器输入口，通过配置在TI1和TI2边沿的计数位置实现所谓的倍频特性，通过向上向下计数实现鉴相，若向上计数往前走，则向下计数则是往后退的过程。由图2和图3知，控制计数点的不同，只能0/2/4倍频。</p>
<p><img src="../images/STM32用作编码器接口的原理/img2.png" alt="img2" /> <img src="../images/STM32用作编码器接口的原理/img3.png" alt="img3" /></p></li>
</ol>
<h2 id="实例代码调试通过">实例代码（调试通过）</h2>
<pre class="sourceCode c"><code class="sourceCode c"><span class="co">/******************************************************************************</span>
<span class="co"> 使用到变量定义</span>
<span class="co">******************************************************************************/</span>
<span class="ot">#define PULSE_PER_CIRCLE 600 </span><span class="co">//编码器分辨率，即转一圈脉冲数</span>
<span class="ot">#define MAX_COUNT 800 </span><span class="co">//最大计数值，解决计数问题时要用</span>
<span class="ot">#define ENCODER_TIM_PERIOD (PULSE_PER_CIRCLE * 4 - 1) </span><span class="co">//定时器周期</span>
SINT32 encoder_last = <span class="dv">0</span>; <span class="co">//记录上一次采集编码器数值</span>
SINT32 encoder_cnt = <span class="dv">0</span>; <span class="co">//编码器采集值</span>
<span class="co">/******************************************************************************</span>
<span class="co"> TIM3定时器配置为编码器模式</span>
<span class="co">******************************************************************************/</span>
<span class="dt">void</span> EncodeInit(<span class="dt">void</span>)
{
GPIO_InitTypeDef GPIO_InitStructure;
TIM_TimeBaseInitTypeDef TIM3_TimeBaseStructure;
TIM_ICInitTypeDef TIM3_ICInitStructure;
<span class="co">/*TIM2 Clock enable*/</span>
RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3, ENABLE);
RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE);
<span class="co">/*Configure PA6,7*/</span>
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_6 | GPIO_Pin_7;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_Init(GPIOA, &GPIO_InitStructure);
<span class="co">/*COnfigure TIM3*/</span>
TIM3_TimeBaseStructure.TIM_Prescaler = <span class="dv">0</span>; <span class="co">//TIM clock = 72MHz </span>
TIM3_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
TIM3_TimeBaseStructure.TIM_Period = ENCODER_TIM_PERIOD;
TIM3_TimeBaseStructure.TIM_ClockDivision = TIM_CKD_DIV1;
TIM3_TimeBaseStructure.TIM_RepetitionCounter = <span class="dv">0</span>;
TIM_TimeBaseInit(TIM3, &TIM3_TimeBaseStructure);
TIM_EncoderInterfaceConfig(TIM3, TIM_EncoderMode_TI12, TIM_ICPolarity_Rising,
TIM_ICPolarity_Rising); <span class="co">//配置编码器模式，4倍频</span>
TIM_ICStructInit(&TIM3_ICInitStructure);
TIM3_ICInitStructure.TIM_ICFilter = <span class="dv">6</span>;
TIM_ICInit(TIM3, &TIM3_ICInitStructure);
<span class="co">/*Reset counter*/</span>
TIM3->CNT = <span class="dv">0</span>;
TIM_Cmd(TIM3, ENABLE);
}</code></pre>
<p>到此，编码器初始化就已经配置好了，按理应该接上就能用了。但是，STM32定时器是16位，假如计数值超过65535，数据会丢失。因此，参考了<http://www.21ic.com>上相关资料。定义32位全局变量存储脉冲数，通过下面的程序技巧实现计数，下面程序是关键。</p>
<pre><code>/*****************************************************************************/
Function Name: ENC_Get_Electrical_Angle
Author : 夏侯佐鑫
Date : 2011-10-22
******************************************************************************/
SINT16 ENC_Get_Electrical_Angle(void)
{
static UINT16 lastCount = 0;
UINT16 curCount = TIM3->CNT;
SINT32 dAngle = curCount - lastCount;
if(dAngle >= MAX_COUNT)
{
dAngle -= ENCODER_TIM_PERIOD;
}
else if(dAngle < -MAX_COUNT)
{
dAngle += ENCODER_TIM_PERIOD;
}
lastCount = curCount;
return (SINT16)dAngle;
}</code></pre>
<p>在SysTick中采集数值，SysTick配置为SysTick_Config(720000)即10ms。SysTick中断函数如下：</p>
<pre><code>/******************************************************************************
Function Name: SysTick_Handler
Author : 夏侯佐鑫
Date : 2011-04-22
******************************************************************************/
void SysTick_Handler(void)
{
/*Encoder*/
encoder_last = encoder_cnt;
encoder_cnt = encoder_cnt + ENC_Get_Electrical_Angle();
}</code></pre>
<p>到此，编码器记里程功能完美实现。此实现代码用于2012年全国电脑鼠走迷宫大赛的电脑鼠制作中。</p>
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