定时器 2
原理图
示例
配置定时器 2：
- 16 位自动重装定时器；
- 时钟源等于内部系统时钟；
- 允许其在计数溢出之后请求中断；
- 每次中断反转一次 P1.1 的输出电平。
main.c 文件：
/**
* STC15W204S-35I SOP16
* Timer 2 - 16 bit, auto-reload
*/
/**
* Interrupt Registers Definition
*/
sfr IE = 0xA8; /* Interrupt Enable Register */
sfr IE2 = 0xAF; /* Interrupt Enable 2 Register */
/**
* Interrupt Registers Bits Definition
*/
/** IE */
#define GLOBAL_IE_EA (0x80)
/** IE2 */
#define T2_IE2_ET2 (0x04) /* Timer 2 interrupt enable */
/**
* Timer 2 Registers Definition
*/
sfr T2L = 0xD7; /* Timer 2 Counter Low Register */
sfr T2H = 0xD6; /* Timer 2 Counter High Register */
sfr AUXR = 0x8E; /* Auxiliary Register */
/**
* Timer 2 Registers Bits Definition
*/
/** AUXR */
#define T2_AUXR_T2R (0x10) /* Timer 2 - Run Control */
#define T2_AUXR_T2CT (0x08) /* Timer 2 - Counter or Timer Selection */
#define T2_AUXR_T2x12 (0x04) /* Timer 2 - Speed Control */
/**
* Port 1 Registers Definition
*/
sfr P1 = 0x90; /* Port 1 Register */
sbit LED = P1^1;
void main() {
AUXR &= ~T2_AUXR_T2CT; // T2 acts as a timer
// AUXR |= T2_AUXR_T2x12; // T2's clock source is divided by 1
T2H = (65536 - 10000) >> 8; // 8 MSB
T2L = (65536 - 10000) & 0xFF; // 8 LSB
AUXR |= T2_AUXR_T2R; // T2 run
IE2 |= T2_IE2_ET2; // Enable T2 overflow interrupt request
IE |= GLOBAL_IE_EA; // Enable global interrupt
while(1) {}
}
void timer2InterruptService() interrupt 12 {
LED = !LED;
}
使用 STC-ISP 下载程序，频率设为 12.000 MHz：
注意：虽然 STC-ISP 提示下载失败！但是，我发现单片机仍然按照我的设想执行程序，这里可能是 STC-ISP 有问题。
对 T2 的时钟源进行 12 分频（AUXR &= ~T2_AUXR_T2x12;），测量 P1.1 输出：
注意：虽然在原理图中，我给单片机的电源符号是 5V，但是在实际测试中，我使用的是 USB 转串口模块上提供的 3.3V（实测没有 3.3V），这并不妨碍单片机正常运行。
不对 T2 的时钟源进行分频（AUXR |= T2_AUXR_T2x12;），测量 P1.1 输出：
模块化处理
把所有的代码写在一个 main.c 文件是非常不好的习惯，我们需要将上例中的定时器 2 模块化处理：
- 将 6 ~ 40 行提取到 stc15w204s.h 头文件中；
- 将 46 ~ 54 行封装成函数，在 timer2.c 文件中实现，在 timer2.h 头文件中声明。
工程结构：
stc15w204s.h 头文件：
- 声明有关定时器 2 的特殊功能寄存器；
- 声明有关定时器 2 的特殊功能寄存器的位掩码；
- 以及其他。
#ifndef __STC15W204S_H
#define __STC15W204S_H
/**
* Interrupt Registers Definition
*/
sfr IE = 0xA8; /* Interrupt Enable Register */
sfr IE2 = 0xAF; /* Interrupt Enable 2 Register */
/**
* Interrupt Registers Bits Definition
*/
/** IE */
#define GLOBAL_IE_EA (0x80)
/** IE2 */
#define T2_IE2_ET2 (0x04) /* Timer 2 interrupt enable */
/**
* Timer 2 Registers Definition
*/
sfr T2L = 0xD7; /* Timer 2 Counter Low Register */
sfr T2H = 0xD6; /* Timer 2 Counter High Register */
sfr AUXR = 0x8E; /* Auxiliary Register */
/**
* Timer 2 Registers Bits Definition
*/
/** AUXR */
#define T2_AUXR_T2R (0x10) /* Timer 2 - Run Control */
#define T2_AUXR_T2CT (0x08) /* Timer 2 - Counter or Timer Selection */
#define T2_AUXR_T2x12 (0x04) /* Timer 2 - Speed Control */
/**
* Port 1 Registers Definition
*/
sfr P1 = 0x90; /* Port 1 Register */
typedef enum {
FALSE = 0,
TRUE = !FALSE
} boolean;
#define enableInterrupts(enable) if(enable) { \
IE |= GLOBAL_IE_EA; \
} else { \
IE &= ~GLOBAL_IE_EA; \
}
#endif
timer2.h 头文件：
#ifndef __STC15W204S_TIMER_2_H
#define __STC15W204S_TIMER_2_H
#include "stc15w204s.h"
typedef enum {
TIMER2_PRESCALER_DIVIDED_BY_1 = ((unsigned char)0x00),
TIMER2_PRESCALER_DIVIDED_BY_12 = ((unsigned char)0x01)
} Timer2Prescaler;
typedef struct {
void (*asTimer)(boolean);
void (*setCounter)(unsigned int);
void (*setTimer)(unsigned int);
void (*setPrescaler)(Timer2Prescaler);
void (*start)(boolean);
void (*enableInterrupt)(boolean);
} Timer2;
extern Timer2 timer2;
/**
* First call to this function to initialize
* the <code>timer2</code> variable.
*/
void Timer2Constructor();
#endif
timer2.c 文件：
#include "timer2.h"
Timer2 timer2;
/**
* If true, timer 2 acts as timer,
* otherwise it acts as counter.
*/
void asTimer(boolean isTimer) {
if(isTimer) {
AUXR &= ~T2_AUXR_T2CT;
} else {
AUXR |= T2_AUXR_T2CT;
}
}
/**
* Set the initial value of the counter
* or the timer.
*/
void setCounter(unsigned int counter) {
T2H = (counter) >> 8;
T2L = (counter) & 0xff;
}
/**
* Set the prescaler of the timer 2.
*/
void setPrescaler(Timer2Prescaler prescaler) {
switch(prescaler) {
case TIMER2_PRESCALER_DIVIDED_BY_1:
AUXR |= T2_AUXR_T2x12;
break;
case TIMER2_PRESCALER_DIVIDED_BY_12:
AUXR &= ~T2_AUXR_T2x12;
break;
}
}
/**
* If true, start the timer 2 to run,
* othewise, stop.
*/
void start(boolean start) {
if(start) {
AUXR |= T2_AUXR_T2R;
} else {
AUXR &= ~T2_AUXR_T2R;
}
}
/**
* If true, enable timer 2 overflow
* interrupt request, othewise, disable.
*/
void enableInterrupt(boolean enable) {
if (enable) {
IE2 |= T2_IE2_ET2;
} else {
IE2 &= ~T2_IE2_ET2;
}
}
/**
* First call to this function to initialize
* the <code>timer2</code> variable.
*/
void Timer2Constructor() {
timer2.asTimer = &asTimer;
timer2.setCounter = &setCounter;
timer2.setTimer = &setCounter;
timer2.setPrescaler = &setPrescaler;
timer2.start = &start;
timer2.enableInterrupt = &enableInterrupt;
}
将定时器 2 的功能模块化处理之后，main.c 文件如下：
/**
* STC15W204S-35I SOP16
* Timer 2 - 16 bit, auto-reload
*/
#include "timer2.h"
sbit LED = P1^1;
void main() {
Timer2Constructor();
timer2.asTimer(TRUE);
timer2.setPrescaler(TIMER2_PRESCALER_DIVIDED_BY_1);
timer2.setTimer(65536 - 10000);
timer2.start(TRUE);
timer2.enableInterrupt(TRUE);
// IE |= GLOBAL_IE_EA; // Enable global interrupt
enableInterrupts(TRUE);
while(1) {}
}
void timer2InterruptService() interrupt 12 {
LED = !LED;
}