diff --git a/src/main.rs b/src/main.rs
index 56c0197..f8ec219 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -36,10 +36,19 @@ fn toggle_mcu_led(gpioa: &mut stm32f103::GPIOA) {
 #[interrupt]
 fn I2C1_EV() {
     cortex_m::interrupt::free(|cs| {
+        static mut BYTES_SENT: u8 = 0;
         if let Some(ref mut i2c1) = *I2C1.borrow(cs).borrow_mut() {
             if i2c1.sr1.read().addr().bit_is_set() {
                 let _ = i2c1.sr2.read();
-                i2c1.dr.write(|w| w.dr().bits(0xAA));
+                i2c1.dr.write(|w| w.dr().bits(0xDE));
+
+                
+                // This should be safe because this this variable
+                // is only written or accessed within this interrupt.
+                unsafe { BYTES_SENT += 1}
+            } else if unsafe {read_volatile(&raw const BYTES_SENT) == 1 } {
+                i2c1.dr.write(|w| w.dr().bits(0xAD));
+                unsafe { BYTES_SENT = 0;}
             }
         }
     });
@@ -94,6 +103,7 @@ fn main() -> ! {
         i2c1.cr2.modify(|_,w| w.itbufen().enabled());
         *I2C1.borrow(cs).borrow_mut() = Some(i2c1);
 
+
         // I don't understand why this is unsafe or how I could make it safe.
         unsafe { cortex_m::peripheral::NVIC::unmask(stm32f1::stm32f103::interrupt::I2C1_EV); }
     });