diff --git a/README.md b/README.md
index d0bce75..b537340 100644
--- a/README.md
+++ b/README.md
@@ -1,6 +1,17 @@
 # chip8-rs
 
 CHIP-8 emulator written in Rust.
-(Done with the Go implementation: https://github.com/arnaucube/go-chip8)
+
+*(Done with the Go implementation: https://github.com/arnaucube/go-chip8)*
 
 https://en.wikipedia.org/wiki/CHIP-8
+
+## Usage
+```
+./chip8-rs --file roms/invaders.c8
+```
+
+![](screenshots/s0.png)
+![](screenshots/s1.png)
+![](screenshots/s2.png)
+![](screenshots/s3.png)
diff --git a/chip8/src/lib.rs b/chip8/src/lib.rs
index f2293d8..99b1bb8 100644
--- a/chip8/src/lib.rs
+++ b/chip8/src/lib.rs
@@ -15,7 +15,7 @@ pub struct Chip8 {
     delay_timer: u8,
     sound_timer: u8,
     stack: [u16; 16],
-    sp: isize,
+    sp: usize,
     pub key: [u8; 16],
     pub draw_flag: bool,
 }
@@ -77,7 +77,7 @@ impl Chip8 {
         let y: usize = ((self.opcode & 0x00F0) >> 4) as usize;
         let nn: u8 = (self.opcode & 0x00FF) as u8;
         let nnn: u16 = (self.opcode & 0x0FFF) as u16;
-        // println!("{:?} {:?}", self.opcode, self.pc);
+        // println!("{:x} {:?}", self.opcode, self.pc);
 
         // Decode Opcode
         // https://en.wikipedia.org/wiki/CHIP-8#Opcode_table
@@ -95,10 +95,10 @@ impl Chip8 {
                     0x000E => {
                         // 00EE Returns from a subroutine
                         self.sp -= 1;
-                        self.pc = self.stack[self.sp as usize];
+                        self.pc = self.stack[self.sp];
                         self.pc += 2;
                     }
-                    _ => println!("unk {:x}", self.opcode),
+                    _ => println!("Unknown opcode: {:x}", self.opcode),
                 }
             }
             0x1000 => {
@@ -107,7 +107,7 @@ impl Chip8 {
             }
             0x2000 => {
                 // 2NNN Calls subroutine at NNN
-                self.stack[self.sp as usize] = self.pc;
+                self.stack[self.sp] = self.pc;
                 self.sp += 1;
                 self.pc = nnn;
             }
@@ -143,7 +143,7 @@ impl Chip8 {
             }
             0x7000 => {
                 // 7XNN Adds NN to VX. (Carry flag is not changed)
-                self.v[x] += nn;
+                self.v[x] = self.v[x].wrapping_add(nn);
                 self.pc += 2;
             }
             0x8000 => {
@@ -176,7 +176,7 @@ impl Chip8 {
                         } else {
                             self.v[0xF] = 0;
                         }
-                        self.v[x] += self.v[y];
+                        self.v[x] = self.v[x].wrapping_add(self.v[y]);
                         self.pc += 2;
                     }
                     0x0005 => {
@@ -187,7 +187,7 @@ impl Chip8 {
                         } else {
                             self.v[0xF] = 0;
                         }
-                        self.v[x] -= self.v[y];
+                        self.v[x] = self.v[x].wrapping_sub(self.v[y]);
                         self.pc += 2;
                     }
                     0x0006 => {
@@ -198,7 +198,7 @@ impl Chip8 {
                         } else {
                             self.v[0xF] = 0;
                         }
-                        self.v[x] = self.v[x] >> 1;
+                        self.v[x] = self.v[x].wrapping_shr(1);
                         self.pc += 2;
                     }
                     0x0007 => {
@@ -209,7 +209,7 @@ impl Chip8 {
                         } else {
                             self.v[0xF] = 0;
                         }
-                        self.v[x] = self.v[y] - self.v[x];
+                        self.v[x] = self.v[y].wrapping_sub(self.v[x]);
                         self.pc += 2;
                     }
                     0x000E => {
@@ -220,10 +220,10 @@ impl Chip8 {
                         } else {
                             self.v[0xF] = 0;
                         }
-                        self.v[x] = self.v[x] << 1;
+                        self.v[x] = self.v[x].wrapping_shl(1);
                         self.pc += 2;
                     }
-                    _ => println!("unk {:x}", self.opcode),
+                    _ => println!("Unknown opcode: {:x}", self.opcode),
                 }
             }
             0x9000 => {
@@ -243,7 +243,7 @@ impl Chip8 {
             0xB000 => {
                 // BNNN Jumps to the address NNN plus V0
                 self.pc = nnn + self.v[0] as u16;
-                self.pc += 2;
+                // self.pc += 2;
             }
             0xC000 => {
                 // CXNN Sets VX to the result of a bitwise and operation on a
@@ -275,9 +275,8 @@ impl Chip8 {
                             }
                             if self.gfx[pos] == 1 {
                                 self.v[0xF] = 1;
-                            } else {
-                                self.gfx[pos] ^= 1;
                             }
+                            self.gfx[pos] ^= 1;
                         }
                     }
                 }
@@ -305,7 +304,7 @@ impl Chip8 {
                         }
                         self.pc += 2;
                     }
-                    _ => println!("unk {:x}", self.opcode),
+                    _ => println!("Unknown opcode: {:x}", self.opcode),
                 }
             }
             0xF000 => {
@@ -378,10 +377,10 @@ impl Chip8 {
                         }
                         self.pc += 2;
                     }
-                    _ => println!("unk {:x}", self.opcode),
+                    _ => println!("Unknown opcode: {:x}", self.opcode),
                 }
             }
-            _ => println!("opc {:x}", self.opcode),
+            _ => println!("Unknown opcode: {:x}", self.opcode),
         }
         if self.delay_timer > 0 {
             self.delay_timer -= 1;
diff --git a/screenshots/s0.png b/screenshots/s0.png
new file mode 100644
index 0000000..21fc911
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diff --git a/screenshots/s1.png b/screenshots/s1.png
new file mode 100644
index 0000000..3161fce
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diff --git a/screenshots/s2.png b/screenshots/s2.png
new file mode 100644
index 0000000..17cd8aa
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diff --git a/screenshots/s3.png b/screenshots/s3.png
new file mode 100644
index 0000000..9a4c564
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diff --git a/src/main.rs b/src/main.rs
index 10c71ec..360b1b1 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -30,7 +30,7 @@ impl SdlEmulator {
         let video_subsystem = sdl_context.video().unwrap();
 
         let window = video_subsystem
-            .window("rust-sdl2 demo", (w * zoom) as u32, (h * zoom) as u32)
+            .window("chip8-rs", (w * zoom) as u32, (h * zoom) as u32)
             .position_centered()
             .build()
             .unwrap();
@@ -45,14 +45,15 @@ impl SdlEmulator {
         vkeys.insert(Keycode::Q, 0x04);
         vkeys.insert(Keycode::W, 0x05);
         vkeys.insert(Keycode::E, 0x06);
-        vkeys.insert(Keycode::R, 0x07);
-        vkeys.insert(Keycode::A, 0x08);
-        vkeys.insert(Keycode::S, 0x09);
-        vkeys.insert(Keycode::D, 0x0E);
-        vkeys.insert(Keycode::F, 0x0A);
-        vkeys.insert(Keycode::Z, 0x00);
-        vkeys.insert(Keycode::X, 0x0B);
-        vkeys.insert(Keycode::V, 0x0F);
+        vkeys.insert(Keycode::R, 0x0d);
+        vkeys.insert(Keycode::A, 0x07);
+        vkeys.insert(Keycode::S, 0x08);
+        vkeys.insert(Keycode::D, 0x09);
+        vkeys.insert(Keycode::F, 0x0e);
+        vkeys.insert(Keycode::Z, 0x0a);
+        vkeys.insert(Keycode::X, 0x00);
+        vkeys.insert(Keycode::C, 0x0b);
+        vkeys.insert(Keycode::V, 0x0f);
 
         SdlEmulator {
             w,
@@ -152,6 +153,6 @@ fn main() {
             e.draw_graphics();
         }
         e.set_keys();
-        std::thread::sleep(time::Duration::from_millis(1000 / 60));
+        std::thread::sleep(time::Duration::from_millis(200 / 60));
     }
 }