diff --git a/C64_4joy_adapter/interrupt_test.ino b/C64_4joy_adapter/interrupt_test.ino
new file mode 100644
index 0000000..b62e6a8
--- /dev/null
+++ b/C64_4joy_adapter/interrupt_test.ino
@@ -0,0 +1,49 @@
+#define LED_PIN 5  // digital pin #13 (portb) (pin #9 with Arduino Pro Micro)
+#define LED_ON() PORTB |= _BV(LED_PIN)
+#define LED_OFF() PORTB &= ~_BV(LED_PIN)
+
+volatile uint8_t output1;
+volatile uint8_t output2;
+
+ISR(INT0_vect, ISR_NAKED)
+{
+    asm volatile(
+    "    push r0                \n"  // save register r0
+    "    lds r0, output1        \n"
+    "    out %[pin], r0         \n"
+    "    pop r0                 \n"  // restore previous r0
+    "    rjmp INT0_vect_part_2  \n"  // go to part 2 for required prologue and epilogue
+    :: [pin] "I" (_SFR_IO_ADDR(PORTB)));
+}
+
+ISR(INT0_vect_part_2) {
+}
+
+ISR(INT1_vect, ISR_NAKED)
+{
+    asm volatile(
+    "    push r0                \n"  // save register r0
+    "    lds r0, output2        \n"
+    "    out %[pin], r0         \n"
+    "    pop r0                 \n"  // restore previous r0
+    "    rjmp INT1_vect_part_2  \n"  // go to part 2 for required prologue and epilogue
+    :: [pin] "I" (_SFR_IO_ADDR(PORTB)));
+}
+
+ISR(INT1_vect_part_2) {
+}
+
+void setup() {
+  //pinMode(13, OUTPUT); // Arduino Uno
+  pinMode(9, OUTPUT); // Arduino Pro Micro
+  TIMSK0 = 0; // disable timer0 interrupts (Arduino Uno/Pro Micro millis() update ISR)
+  EICRA = B1011;  // INT0 – rising edge on 2 (B11), INT1 - falling edge on 3 (B10xx)
+  EIMSK = B11;  // enable int0 (Bx1) and int1 (B1x)
+}
+
+void loop() {
+  LED_ON();
+  //LED_OFF();
+  output1 = 0;
+  delayMicroseconds(50);
+}