Hi! I've many interrupt service routines on my current project! But I didn't succeed in passing data between the main function and the ISRs! I declared global variables (no difference if static or not), but when the ISR is invoked, the value of the variables is 0xFF (unsigned char) oder 0xFFFF (unsigned int)! On the compiler the "small" memory model is selected! Any idea, what's wrong? Have a nice day! SVEN
Globals are usually evil but if you do use them to share data or control between the main line code and an ISR, be sure to declare them volatile. Usually, only one C file has a need for such a variable so you should limit the variables scope with the static keyword so they are not project global.
volatile static unsigned char s_rdIdx; volatile static unsigned char s_wrIdx; void uartIsr(void) interrupt UART using 1 { if (RI) { RI = 0; if (s_wrIdx == s_rdIdx) { // Ring is full } } } int getchar(void) { char inChar; // Wait while ring is empty. while (s_rdIdx == s_wrIdx); ... return (int) inChar; }