diff --git a/src/cpu.ml b/src/cpu.ml
index 27295e5..3b20f23 100644
--- a/src/cpu.ml
+++ b/src/cpu.ml
@@ -76,7 +76,7 @@ let update_flag_reg cpu =
   cpu.reg.f <- char_of_int @@ z + n + h + c
 
 let inc_pc cpu count =
-  cpu.reg.pc <- cpu.reg.pc + count
+  cpu.reg.pc <- (cpu.reg.pc + count) mod 0xFFFF
 
 let inc_cycles cpu count =
   cpu.cycles <- cpu.cycles + count
@@ -118,6 +118,14 @@ let read_pc_2bytes cpu mem =
   inc_pc cpu 2;
   word
 
+let pop_stack cpu mem =
+  let low = Memory.get mem cpu.reg.sp in
+  cpu.reg.sp <- (cpu.reg.sp + 1) mod 0xFFFF;
+  let high = Memory.get mem cpu.reg.sp in
+  cpu.reg.sp <- (cpu.reg.sp + 1) mod 0xFFFF;
+  merge_bytes low high
+
+
 
 (**
   http://imrannazar.com/GameBoy-Z80-Opcode-Map
@@ -135,12 +143,35 @@ let run cpu (mem: Memory.map) =
   | '\x7E' -> printf "  LD \tA, (HL)\n";
               let hl = merge_bytes cpu.reg.l cpu.reg.h in
               cpu.reg.a <- Memory.get mem hl;
-              inc_cycles cpu 8;
+              inc_cycles cpu 8
+
+  | '\x36' -> let n = read_pc_byte cpu mem in
+              printf "  LD \t(HL) 0x%02X\n" n;
+              let hl = merge_bytes cpu.reg.l cpu.reg.h in
+              Memory.set mem hl (char_of_int n);
+              inc_cycles cpu 12
 
 
+  (* CPU control *)
   | '\x00' -> printf "  NOP\n";
               inc_cycles cpu 4
 
+
+  (* jump *)
+  | '\xC9' -> printf "  RET\n";
+              cpu.reg.pc <- pop_stack cpu mem;
+              inc_cycles cpu 16
+
+  | '\xC0' -> printf "  RET \tNZ\n";
+              if cpu.flag.z = false then
+              begin
+                cpu.reg.pc <- pop_stack cpu mem;
+                inc_cycles cpu 20
+              end else
+                inc_cycles cpu 8
+
+
+
   | '\x03' -> printf "  INC \tBC\n";
               inc_BC cpu;
               inc_cycles cpu 8
@@ -218,14 +249,6 @@ 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_pc_2bytes cpu mem in
               printf "  JP \t0x%04X\n" addr;
               cpu.reg.pc <- addr; inc_cycles cpu 16