Create readme.md

ATTiny2313 2018-02-25 button interrupt/readme.md

@@ -0,0 +1,25 @@
+# Button Press Launches Interrupt
+Here a button (pulled high, grounded when pressed) causes an interrupt.
+
+```C
+
+#include <avr/interrupt.h>
+
+ISR(INT0_vect){
+    // runs when the button is pressed
+}
+
+void SetupButton(){
+  MCUCR=(1<<ISC01); // falling edge of INT0 generates interrupt
+  GIMSK=(1<<INT0); // INT0 causes interrupt request
+  EIFR=(1<<INTF0); // INT0 change Interrupt Flag
+  PCMSK=(1<<PCINT1); // watch these pins
+  sei(); // enable global interrupts
+}
+
+
+int main(void){
+    SetupButton();
+    for(;;){}
+}
+```