diff --git a/src/cpu.rs b/src/cpu.rs
index 40d0f56..8e2ce97 100644
--- a/src/cpu.rs
+++ b/src/cpu.rs
@@ -1,4 +1,4 @@
-use crate::cpu;
+// use crate::cpu;
 use rand::{self, RngExt};
 
 const FONT: [u8; 80] = [
@@ -30,6 +30,7 @@ pub struct Cpu {
     delay_timer: u8,
     sound_timer: u8,
     pub keys: [bool; 16],
+    pub prev_keys: [bool; 16],
 }
 
 impl Cpu {
@@ -45,6 +46,7 @@ impl Cpu {
             delay_timer: 0,
             sound_timer: 0,
             keys: [false; 16],
+            prev_keys: [false; 16],
         };
         cpu.load_font();
         cpu.load_rom(rom);
@@ -139,9 +141,10 @@ impl Cpu {
                     self.reg[x] = result;
                     self.reg[0xF] = not_borrow;
                 }
-                0xE => {    //8xyE - SHL Vx {, Vy}
-                            //Set Vx = Vx SHL 1.
-                            //If the most-significant bit of Vx is 1, then VF is set to 1, otherwise to 0. Then Vx is multiplied by 2.
+                0xE => {
+                    //8xyE - SHL Vx {, Vy}
+                    //Set Vx = Vx SHL 1.
+                    //If the most-significant bit of Vx is 1, then VF is set to 1, otherwise to 0. Then Vx is multiplied by 2.
                     self.reg[x] = self.reg[y];
                     let msb = (self.reg[x] >> 7) & 1;
                     self.reg[x] <<= 1;
@@ -200,15 +203,33 @@ impl Cpu {
             },
             0xF => match nn {
                 0x07 => self.reg[x] = self.delay_timer,
-                0x0A => {}
+                0x0A => {
+                    // this is supposed to block execution until a key is pressed
+                    let mut released_key = None;
+                    for i in 0..16 {
+                        // If it was pressed in the previous frame but is NOT pressed now
+                        if self.prev_keys[i] && !self.keys[i] {
+                            released_key = Some(i as u8);
+                            break;
+                        }
+                    }
+
+                    if let Some(key_code) = released_key {
+                        self.reg[x] = key_code;
+                    } else {
+                        // Not released yet? Stay on this instruction.
+                        self.program_counter -= 2;
+                    }
+                }
                 0x15 => self.delay_timer = self.reg[x],
                 0x18 => self.sound_timer = self.reg[x],
                 0x1E => self.index = self.index.wrapping_add(self.reg[x] as u16),
                 0x29 => {
                     self.index = ((self.reg[x] * 5) + 0x050) as u16;
                 }
-                0x33 => {   // BCD conversion isn't something I've encountered before
-                            // Very interesting op
+                0x33 => {
+                    // BCD conversion isn't something I've encountered before
+                    // Very interesting op
                     let vx = self.reg[x];
                     let hundreds = vx / 100;
                     let tens = (vx / 10) % 10;
diff --git a/src/main.rs b/src/main.rs
index 83ccdb8..3ef2e45 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -25,30 +25,34 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
         },
     )
     .unwrap();
-    let keys = [
-        window.is_key_down(Key::X),    // 0
-        window.is_key_down(Key::Key1), // 1
-        window.is_key_down(Key::Key2), // 2
-        window.is_key_down(Key::Key3), // 3
-        window.is_key_down(Key::Q),    // 4
-        window.is_key_down(Key::W),    // 5
-        window.is_key_down(Key::E),    // 6
-        window.is_key_down(Key::A),    // 7
-        window.is_key_down(Key::S),    // 8
-        window.is_key_down(Key::D),    // 9
-        window.is_key_down(Key::Z),    // A
-        window.is_key_down(Key::C),    // B
-        window.is_key_down(Key::Key4), // C
-        window.is_key_down(Key::R),    // D
-        window.is_key_down(Key::F),    // E
-        window.is_key_down(Key::V),    // F
-    ];
 
     let mut buffer: Vec<u32> = vec![0; WIDTH * HEIGHT];
 
     while window.is_open() {
+        let keys = [
+            window.is_key_down(Key::X),    // 0
+            window.is_key_down(Key::Key1), // 1
+            window.is_key_down(Key::Key2), // 2
+            window.is_key_down(Key::Key3), // 3
+            window.is_key_down(Key::Q),    // 4
+            window.is_key_down(Key::W),    // 5
+            window.is_key_down(Key::E),    // 6
+            window.is_key_down(Key::A),    // 7
+            window.is_key_down(Key::S),    // 8
+            window.is_key_down(Key::D),    // 9
+            window.is_key_down(Key::Z),    // A
+            window.is_key_down(Key::C),    // B
+            window.is_key_down(Key::Key4), // C
+            window.is_key_down(Key::R),    // D
+            window.is_key_down(Key::F),    // E
+            window.is_key_down(Key::V),    // F
+        ];
+        chip8.prev_keys = chip8.keys;
         chip8.keys = keys;
-        chip8.tick();
+        for _ in 0..10 {
+            // 10 ticks * 60fps = ~600 cycles/sec
+            chip8.tick();
+        }
         for (i, pixel) in chip8.display.iter().enumerate() {
             buffer[i] = if *pixel { 0xFFFFFFFF } else { 0x00000000 };
         }