diff --git a/simulator.js b/simulator.js
index bf80c9a..7b2c646 100644
--- a/simulator.js
+++ b/simulator.js
@@ -10,9 +10,14 @@ const CPU = {
   Acc: 0,
   memory: null,
   loadMemory: (data) => { // data: Uint8Array
-    // TODO: check length of data
+    if (data.length > 256) { throw new Error("Out of memory error (program too long)"); }
     CPU.memory = data;
   },
+  currentInstruction: {
+    opcode: null,
+    argument: null,
+    mnemonic: null,
+  }
 }