diff --git a/Cargo.lock b/Cargo.lock
index 495c3d5..a4fcddd 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -13,4 +13,20 @@ name = "lc3"
 version = "0.1.0"
 dependencies = [
  "byteorder",
+ "termios",
+]
+
+[[package]]
+name = "libc"
+version = "0.2.151"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "302d7ab3130588088d277783b1e2d2e10c9e9e4a16dd9050e6ec93fb3e7048f4"
+
+[[package]]
+name = "termios"
+version = "0.3.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "411c5bf740737c7918b8b1fe232dca4dc9f8e754b8ad5e20966814001ed0ac6b"
+dependencies = [
+ "libc",
 ]
diff --git a/Cargo.toml b/Cargo.toml
index ecf7be9..62d08be 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -7,3 +7,4 @@ edition = "2021"
 
 [dependencies]
 byteorder = "1.5.0"
+termios = "0.3.3"
diff --git a/src/vm/memory.rs b/src/vm/memory.rs
new file mode 100644
index 0000000..27ab6e9
--- /dev/null
+++ b/src/vm/memory.rs
@@ -0,0 +1,32 @@
+//////////////////////////////
+////// memory and memory-mapped registers
+//////////////////////////////
+
+////////////////
+// memory interface
+////////////////
+
+pub const MEM_SIZE: usize = 1 << 16;
+
+pub struct Memory {
+    data: [u16; MEM_SIZE],
+}
+
+impl Memory {
+    pub fn new() -> Memory {
+        Memory {
+            data: [0; MEM_SIZE],
+        }
+    }
+
+    pub fn set_mem(&mut self, addr: u16, val: u16) {
+        self.data[addr as usize] = val;
+    }
+
+    pub fn get_mem(&self, addr: u16) -> u16 {
+        if addr >= 0xFE00 {
+            unimplemented!("mem-map: {:#X}", addr);
+        }
+        return self.data[addr as usize];
+    }
+}
diff --git a/src/vm/mod.rs b/src/vm/mod.rs
index efbe191..0c67a04 100644
--- a/src/vm/mod.rs
+++ b/src/vm/mod.rs
@@ -12,13 +12,14 @@ use byteorder::{BigEndian, ReadBytesExt};
 use std::{fs::File, io::BufReader};
 
 mod instruction;
+mod memory;
 
 ////////////////
 // registers
 ////////////////
 
 // condition flags (COND register)
-pub enum CondFlags {
+enum CondFlags {
     // positive (P)
     POS = 1 << 0,
     // zero (Z)
@@ -105,38 +106,12 @@ impl Registers {
     }
 }
 
-////////////////
-// memory
-////////////////
-
-const MEM_SIZE: usize = 1 << 16;
-
-struct Memory {
-    data: [u16; MEM_SIZE],
-}
-
-impl Memory {
-    fn new() -> Memory {
-        Memory {
-            data: [0; MEM_SIZE],
-        }
-    }
-
-    fn set_mem(&mut self, addr: u16, val: u16) {
-        self.data[addr as usize] = val;
-    }
-
-    fn get_mem(&self, addr: u16) -> u16 {
-        return self.data[addr as usize];
-    }
-}
-
 ////////////////
 // VM interface
 ////////////////
 
 pub struct VM {
-    mem: Memory,
+    mem: memory::Memory,
     registers: Registers,
     running: bool,
 }
@@ -144,7 +119,7 @@ pub struct VM {
 impl VM {
     pub fn new() -> VM {
         VM {
-            mem: Memory::new(),
+            mem: memory::Memory::new(),
             registers: Registers::new(),
             running: false,
         }
@@ -198,7 +173,7 @@ impl VM {
             // remember PC points to the *next* instruction at all times
 
             // disallow reading past memory bounds
-            if self.registers.pc as usize == MEM_SIZE - 1 {
+            if self.registers.pc as usize == memory::MEM_SIZE - 1 {
                 self.running = false
             } else {
                 self.registers.pc += 1;