Reading falling / rising edges without using interrupt on change

惨淡的人生

电梯直达[url=][/url] 1楼 发表于 2010-7-28 08:26:02 | 只看该作者 a lot of times, you want to read if a pin has gone through a transition (high->low, or low->high). some times, your mcu may have interrupt-on-change functionality for that. for those mcus that do not have IOC functionality, or you don't have space for IOC, you can implement it fairly easily, as shown below. =========code=============== #define PORT_TYPE                        unsigned int                //works for 32-bit ports //#define PORT_TYPE                        unsigned char                //works for 8-bit ports //set bits where the pins have gone through a low-high or high-low transition PORT_TYPE port_get_changing(PORT_TYPE port, PORT_TYPE pins) {         PORT_TYPE tmp;         static PORT_TYPE pins_prev=0x00;         tmp=pins_prev;                                        //save pins_prev         pins_prev=port & pins;                        //read pins from port         return (pins_prev ^ tmp);                //return rising or falling edge } //return 1 on bits where the pins have gone through a high-low transition PORT_TYPE port_get_falling(PORT_TYPE port, PORT_TYPE pins) {         PORT_TYPE tmp;         static PORT_TYPE pins_prev=0x00;         tmp=pins_prev;                                        //save pins_prev         pins_prev=port & pins;                        //read pins from port         return (pins_prev ^ tmp) & tmp;        //return falling edge } //set bits where the pins have gone through a low-high transistion PORT_TYPE port_get_rising(PORT_TYPE port, PORT_TYPE pins) {         PORT_TYPE tmp;         static PORT_TYPE pins_prev=0x00;         tmp=pins_prev;                                        //save pins_prev         pins_prev=port & pins;                        //read pins from port         return (pins_prev ^ tmp) & pins_prev;        //return rising edge } ===========end of code============ port_get_rising(port, pins) will return 0x08 if port.7 has gone through a low->high transition. similarly, port_get_changing(port, pins) will return 0x28 if port.9 and port.7 have gone through either a high->low or low->high transition. here is a piece of code that demonstrates how it works. =====demo code=========== //demo program int main(void) {                                        //main         mcu_init();         while (1) {                 if (port_get_changing(KEY_PORT, KEYs) & KEY1) IO_FLP(LED_PORT, LED1);          //flip led1 where key1 has changed                 if (port_get_falling(KEY_PORT, KEYs) & KEYs)  IO_FLP(LED_PORT, LED2);        //flip led2 when key1 or key2 goes high->low                 if (port_get_rising(KEY_PORT, KEYs) & KEY2)   IO_FLP(LED_PORT, LED3);        //flip led3 when key2 goes low->high                 //do something else         } } =========end code========== KEY1 and KEY2 are two input sources that go from 0->1 and then 1->0 at varying frequencies. LED1 is programmed to flip its state whenever KEY1 has gone through a transition; LED2 flips if either KEY1 or KEY2 goes from high to low; LED3 flips only if KEY2 goes low->high. here is the simulation. (原文件名PC2106 get_key.PNG) since the code is entirely C, it is highly portable to other platforms. enjoy.