以下是一個STC官方給的一個例程，使用PCA實現定時器的功能，在實際使用中沒什么問題，但一直有一個疑問沒有搞明白，就是那個增加的步長value
定義的是一個無符號的整型變量，在整個代碼中value一直在自增，沒有清過0，value不會溢出么？很是好奇
/*---------------------------------------------------------------------*/
/* --- STC MCU Limited ------------------------------------------------*/
/* --- STC15F4K60S4 系列 PCA實現16位定時器舉例-------------------------*/
/* --- Mobile: (86)13922805190 ----------------------------------------*/
/* 如果要在程序中使用此代碼,請在程序中注明使用了STC的資料及程序 */
/* 如果要在文章中應用此代碼,請在文章中注明使用了STC的資料及程序 */
/*---------------------------------------------------------------------*/
//本示例在Keil開發環境下請選擇Intel的8058芯片型號進行編譯
//若無特別說明,工作頻率一般為11.0592MHz
#include "reg51.h"
#include "intrins.h"
#define FOSC 11059200L
#define T100Hz (FOSC / 12 / 100)
typedef unsigned char BYTE;
typedef unsigned int WORD;
sfr P0M1 = 0x93;
sfr P0M0 = 0x94;
sfr P1M1 = 0x91;
sfr P1M0 = 0x92;
sfr P2M1 = 0x95;
sfr P2M0 = 0x96;
sfr P3M1 = 0xb1;
sfr P3M0 = 0xb2;
sfr P4M1 = 0xb3;
sfr P4M0 = 0xb4;
sfr P5M1 = 0xC9;
sfr P5M0 = 0xCA;
sfr P6M1 = 0xCB;
sfr P6M0 = 0xCC;
sfr P7M1 = 0xE1;
sfr P7M0 = 0xE2;
sfr P_SW1 = 0xA2; //外設功能切換寄存器1
#define CCP_S0 0x10 //P_SW1.4
#define CCP_S1 0x20 //P_SW1.5
sfr CCON = 0xD8; //PCA控制寄存器
sbit CCF0 = CCON^0; //PCA模塊0中斷標志
sbit CCF1 = CCON^1; //PCA模塊1中斷標志
sbit CR = CCON^6; //PCA定時器運行控制位
sbit CF = CCON^7; //PCA定時器溢出標志
sfr CMOD = 0xD9; //PCA模式寄存器
sfr CL = 0xE9; //PCA定時器低字節
sfr CH = 0xF9; //PCA定時器高字節
sfr CCAPM0 = 0xDA; //PCA模塊0模式寄存器
sfr CCAP0L = 0xEA; //PCA模塊0捕獲寄存器 LOW
sfr CCAP0H = 0xFA; //PCA模塊0捕獲寄存器 HIGH
sfr CCAPM1 = 0xDB; //PCA模塊1模式寄存器
sfr CCAP1L = 0xEB; //PCA模塊1捕獲寄存器 LOW
sfr CCAP1H = 0xFB; //PCA模塊1捕獲寄存器 HIGH
sfr PCAPWM0 = 0xf2;
sfr PCAPWM1 = 0xf3;
sbit PCA_LED = P1^0; //PCA測試LED
BYTE cnt;
WORD value;
void PCA_isr() interrupt 7 using 1
{
CCF0 = 0; //清中斷標志
CCAP0L = value;
CCAP0H = value >> 8; //更新比較值
value += T100Hz;
if (cnt-- == 0)
{
cnt = 100; //記數100次
PCA_LED = !PCA_LED; //每秒閃爍一次
}
}
void main()
{
P0M0 = 0x00;
P0M1 = 0x00;
P1M0 = 0x00;
P1M1 = 0x00;
P2M0 = 0x00;
P2M1 = 0x00;
P3M0 = 0x00;
P3M1 = 0x00;
P4M0 = 0x00;
P4M1 = 0x00;
P5M0 = 0x00;
P5M1 = 0x00;
P6M0 = 0x00;
P6M1 = 0x00;
P7M0 = 0x00;
P7M1 = 0x00;
ACC = P_SW1;
ACC &= ~(CCP_S0 | CCP_S1); //CCP_S0=0 CCP_S1=0
P_SW1 = ACC; //(P1.2/ECI, P1.1/CCP0, P1.0/CCP1, P3.7/CCP2)
// ACC = P_SW1;
// ACC &= ~(CCP_S0 | CCP_S1); //CCP_S0=1 CCP_S1=0
// ACC |= CCP_S0; //(P3.4/ECI_2, P3.5/CCP0_2, P3.6/CCP1_2, P3.7/CCP2_2)
// P_SW1 = ACC;
//
// ACC = P_SW1;
// ACC &= ~(CCP_S0 | CCP_S1); //CCP_S0=0 CCP_S1=1
// ACC |= CCP_S1; //(P2.4/ECI_3, P2.5/CCP0_3, P2.6/CCP1_3, P2.7/CCP2_3)
// P_SW1 = ACC;
CCON = 0; //初始化PCA控制寄存器
//PCA定時器停止
//清除CF標志
//清除模塊中斷標志
CL = 0; //復位PCA寄存器
CH = 0;
CMOD = 0x00; //設置PCA時鐘源
//禁止PCA定時器溢出中斷
value = T100Hz;
CCAP0L = value;
CCAP0H = value >> 8; //初始化PCA模塊0
value += T100Hz;
CCAPM0 = 0x49; //PCA模塊0為16位定時器模式
CR = 1; //PCA定時器開始工作
EA = 1;
cnt = 0;
while (1);
}
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