diff --git a/src/cpu.ml b/src/cpu.ml
index 8f42fc1..861e2e2 100644
--- a/src/cpu.ml
+++ b/src/cpu.ml
@@ -17,15 +17,16 @@ type registers = {
   mutable pc : int; (* program counter *)
 }
 
-(* type flags = {
-  z  : bool; (* zero *)
-  n  : bool; (* substraction *)
-  h  : bool; (* half-carry *)
-  cy : bool; (* carry *)
-} *)
+ type flags = {
+  mutable z : bool; (* zero *)
+  mutable n : bool; (* substraction *)
+  mutable h : bool; (* half-carry *)
+  mutable c : bool; (* carry *)
+}
 
 type t = {
   reg : registers;
+  flag : flags;
   mutable cycles : int;
 }
 
@@ -44,8 +45,20 @@ let init_registers =
     pc = 0x0100;
   }
 
+let init_flags =
+  {
+    z = false; n = false; h = false; c = false
+  }
+
 let init_cpu =
-  { reg = init_registers; cycles = 0 }
+  { reg = init_registers; flag = init_flags; cycles = 0 }
+
+let update_flag_reg cpu =
+  let z = if cpu.flag.z then 0b10000000 else 0 in
+  let n = if cpu.flag.n then 0b01000000 else 0 in
+  let h = if cpu.flag.h then 0b00100000 else 0 in
+  let c = if cpu.flag.c then 0b00010000 else 0 in
+  cpu.reg.f <- char_of_int @@ z + n + h + c
 
 let inc_pc cpu count =
   cpu.reg.pc <- cpu.reg.pc + count
@@ -72,10 +85,18 @@ let inc_BC cpu =
   cpu.reg.c <- low;
   cpu.reg.b <- high
 
+let cmp_A cpu n =
+  let diff = int_of_char (cpu.reg.a) - n in
+  cpu.flag.z <- diff = 0;
+  cpu.flag.n <- true;
+  cpu.flag.h <- diff > 0x0F || diff < 0;
+  cpu.flag.c <- diff > 0xFF || diff < 0;
+  update_flag_reg cpu
+
 (** http://imrannazar.com/GameBoy-Z80-Opcode-Map *)
 let run cpu (mem: Memory.map) =
-  let n = Memory.get mem (cpu.reg.pc + 1) in
-  let nn = Memory.get mem (cpu.reg.pc + 2) in
+  let n = Memory.get mem (cpu.reg.pc + 1) |> int_of_char in
+(*  let nn = Memory.get mem (cpu.reg.pc + 2) in *)
 (*  Hexa.print_slice cartridge.full_rom cpu.reg.pc (cpu.reg.pc + 7); *)
   match Memory.get mem cpu.reg.pc with
   | '\x00' -> printf "  NOP\n";
@@ -85,8 +106,8 @@ let run cpu (mem: Memory.map) =
               inc_BC cpu;
               inc_pc cpu 1; inc_cycles cpu 8
 
-  | '\x3E' -> printf "  LD \tA, 0x%02X\n" (int_of_char n);
-              cpu.reg.a <- n;
+  | '\x3E' -> printf "  LD \tA, 0x%02X\n" n;
+              cpu.reg.a <- char_of_int(n);
               inc_pc cpu 2; inc_cycles cpu 8
 
   | '\xAF' -> printf "  XOR \tA, A\n";
@@ -98,16 +119,20 @@ let run cpu (mem: Memory.map) =
               printf "  JP \t0x%04X\n" addr;
               cpu.reg.pc <- addr; inc_cycles cpu 16
 
-  | '\xE0' -> printf "  LDH \t(0xFF%02X), A\n" (int_of_char n);
-              Memory.set mem (0xFF00 + (int_of_char n)) cpu.reg.a;
+  | '\xE0' -> printf "  LDH \t(0xFF%02X), A\n" n;
+              Memory.set mem (0xFF00 + n) cpu.reg.a;
               inc_pc cpu 2; inc_cycles cpu 12
 
-  | '\xF0' -> printf "  LDH \tA, (0xFF%02X)\n" (int_of_char n);
-              cpu.reg.a = Memory.get mem (0xFF00 + (int_of_char n));
+  | '\xF0' -> printf "  LDH \tA, (0xFF%02X)\n" n;
+              cpu.reg.a <- Memory.get mem (0xFF00 + n);
               inc_pc cpu 2; inc_cycles cpu 12
 
   | '\xF3' -> printf "  DI\n";
               (* fixme *)
               inc_pc cpu 1; inc_cycles cpu 4
 
+  | '\xFE' -> printf "  CP\t0x%02X\n" n;
+              cmp_A cpu n;
+              inc_pc cpu 2; inc_cycles cpu 8
+
   | _ as x -> eprintf "opcode %02X\n" (int_of_char x); failwith "Unimplemented opcode."
diff --git a/src/memory.ml b/src/memory.ml
index 785c170..5bba426 100644
--- a/src/memory.ml
+++ b/src/memory.ml
@@ -8,6 +8,8 @@ type map = {
   rom_bank_01 : bytes; (* additional bank, 16KB *)
   vram : bytes; (* Video RAM, 8KB *)
   io : bytes; (* I/O ports *)
+  hram : bytes; (* High RAM, 8KB *)
+  interrupt : bytes; (* Interrupt Enable Register *)
 }
 
 let init (cartridge: Cartridge.t) =
@@ -16,6 +18,8 @@ let init (cartridge: Cartridge.t) =
     rom_bank_01 = create 0x4000;
     vram = create 0x2000;
     io = create 0x0080;
+    hram = create 0x2000;
+    interrupt = create 1
   }
 
 let get_mem_bank mem addr =
@@ -25,6 +29,8 @@ let get_mem_bank mem addr =
   | x when x < 0xA000 -> mem.vram,  (x - 0x8000)
   | x when x < 0xFF00 -> failwith "Unimplemented memory range."
   | x when x < 0xFF80 -> mem.io, x - 0xFF00
+  | x when x < 0xFFFF -> mem.hram, x - 0xFF80
+  | 0xFFFF -> mem.interrupt, 0
   | _ -> failwith "Invalid memory range."