diff --git a/src/cpu.ml b/src/cpu.ml
index 294a767..d2dc4e9 100644
--- a/src/cpu.ml
+++ b/src/cpu.ml
@@ -93,12 +93,15 @@ let cmp_A cpu n =
   cpu.flag.c <- diff > 0xFF || diff < 0;
   update_flag_reg cpu
 
-(** http://imrannazar.com/GameBoy-Z80-Opcode-Map *)
+(**
+  http://imrannazar.com/GameBoy-Z80-Opcode-Map
+  https://github.com/sinamas/gambatte/blob/master/libgambatte/src/cpu.cpp
+*)
 let run cpu (mem: Memory.map) =
   let opcode = Memory.get mem cpu.reg.pc in
   inc_pc cpu 1;
   let n = Memory.get mem cpu.reg.pc |> int_of_char in
-(*  let nn = Memory.get mem (cpu.reg.pc + 2) in *)
+  let nn = Memory.get mem (cpu.reg.pc + 1) |> int_of_char in
 (*  Hexa.print_slice cartridge.full_rom cpu.reg.pc (cpu.reg.pc + 7); *)
   match opcode with
   | '\x00' -> printf "  NOP\n";
@@ -108,6 +111,9 @@ let run cpu (mem: Memory.map) =
               inc_BC cpu;
               inc_cycles cpu 8
 
+  | '\x18' -> printf "  JP\t 0x%02X\n" n;
+              inc_pc cpu n; inc_cycles cpu 12
+
   | '\x20' -> printf "  JR\t NZ, 0x%02X\n" n;
               if cpu.flag.z = false then
               begin
@@ -117,6 +123,23 @@ let run cpu (mem: Memory.map) =
                 inc_pc cpu 1; inc_cycles cpu 8
               end
 
+  | '\x21' -> let addr = read_2B mem cpu.reg.pc in
+              printf "  LD\t HL, 0x%04X\n" addr;
+              cpu.reg.h <- char_of_int nn;
+              cpu.reg.l <- char_of_int n;
+              inc_cycles cpu 12
+
+
+  | '\x28' -> printf "  JR\t Z, 0x%02X\n" n;
+              if cpu.flag.z = true then
+              begin
+                inc_pc cpu n; inc_cycles cpu 12
+              end else
+              begin
+                inc_pc cpu 1; inc_cycles cpu 8
+              end
+
+
   | '\x3E' -> printf "  LD \tA, 0x%02X\n" n;
               cpu.reg.a <- char_of_int(n);
               inc_pc cpu 1; inc_cycles cpu 8
@@ -126,6 +149,14 @@ let run cpu (mem: Memory.map) =
               cpu.reg.a <- char_of_int @@ int_A lxor int_A;
               inc_cycles cpu 4
 
+  | '\xC0' -> printf "  RET \tNZ\n";
+              if cpu.flag.z = false then
+              begin
+                cpu.reg.pc <- cpu.reg.sp;
+                inc_cycles cpu 20
+              end else
+                inc_cycles cpu 8
+
   | '\xC3' -> let addr = read_2B mem cpu.reg.pc in
               printf "  JP \t0x%04X\n" addr;
               cpu.reg.pc <- addr; inc_cycles cpu 16
@@ -146,5 +177,5 @@ let run cpu (mem: Memory.map) =
               cmp_A cpu n;
               inc_pc cpu 1; inc_cycles cpu 8
 
-  | _ as x -> eprintf "opcode %02X\n" (int_of_char x);
-              failwith "Unimplemented opcode."
+  |  x -> eprintf "opcode 0x%02X\n" (int_of_char x);
+          failwith "Unimplemented opcode."
diff --git a/src/memory.ml b/src/memory.ml
index 5bba426..c6ced06 100644
--- a/src/memory.ml
+++ b/src/memory.ml
@@ -1,4 +1,5 @@
 open Bytes
+open Printf
 
 (** http://bgb.bircd.org/pandocs.htm#memorymap
     http://imrannazar.com/GameBoy-Emulation-in-JavaScript:-Memory *)
@@ -31,7 +32,8 @@ let get_mem_bank mem addr =
   | x when x < 0xFF80 -> mem.io, x - 0xFF00
   | x when x < 0xFFFF -> mem.hram, x - 0xFF80
   | 0xFFFF -> mem.interrupt, 0
-  | _ -> failwith "Invalid memory range."
+  | x -> eprintf "Memory access 0x%08X\n" x;
+         failwith "Invalid memory range."
 
 
 let get mem addr =