diff --git a/DisplaySDL.hpp b/DisplaySDL.hpp
index 6f88350..6fd87e9 100644
--- a/DisplaySDL.hpp
+++ b/DisplaySDL.hpp
@@ -7,7 +7,7 @@
 
 class DisplaySDL : public chocochip8::Display {
 public:
-  DisplaySDL(int w, int h, uint32_t fgCol, uint32_t bgCol);
+  DisplaySDL(int w, int h, uint32_t fgCol = 0xffffff, uint32_t bgCol = 0x000000);
   ~DisplaySDL() override;
   void updateWindow() const;
 
diff --git a/Interpreter.cpp b/Interpreter.cpp
index bde7e81..dba54f0 100644
--- a/Interpreter.cpp
+++ b/Interpreter.cpp
@@ -4,6 +4,44 @@
 
 namespace chocochip8 {
 
+constexpr uint16_t gcvLowResToHighResRowLookupTable[256] = {
+  0x0000, 0x0003, 0x000C, 0x000F, 0x0030, 0x0033, 0x003C, 0x003F, 0x00C0, 0x00C3, 0x00CC, 0x00CF, 0x00F0, 0x00F3, 0x00FC, 0x00FF, 
+  0x0300, 0x0303, 0x030C, 0x030F, 0x0330, 0x0333, 0x033C, 0x033F, 0x03C0, 0x03C3, 0x03CC, 0x03CF, 0x03F0, 0x03F3, 0x03FC, 0x03FF, 
+  0x0C00, 0x0C03, 0x0C0C, 0x0C0F, 0x0C30, 0x0C33, 0x0C3C, 0x0C3F, 0x0CC0, 0x0CC3, 0x0CCC, 0x0CCF, 0x0CF0, 0x0CF3, 0x0CFC, 0x0CFF, 
+  0x0F00, 0x0F03, 0x0F0C, 0x0F0F, 0x0F30, 0x0F33, 0x0F3C, 0x0F3F, 0x0FC0, 0x0FC3, 0x0FCC, 0x0FCF, 0x0FF0, 0x0FF3, 0x0FFC, 0x0FFF, 
+  0x3000, 0x3003, 0x300C, 0x300F, 0x3030, 0x3033, 0x303C, 0x303F, 0x30C0, 0x30C3, 0x30CC, 0x30CF, 0x30F0, 0x30F3, 0x30FC, 0x30FF, 
+  0x3300, 0x3303, 0x330C, 0x330F, 0x3330, 0x3333, 0x333C, 0x333F, 0x33C0, 0x33C3, 0x33CC, 0x33CF, 0x33F0, 0x33F3, 0x33FC, 0x33FF, 
+  0x3C00, 0x3C03, 0x3C0C, 0x3C0F, 0x3C30, 0x3C33, 0x3C3C, 0x3C3F, 0x3CC0, 0x3CC3, 0x3CCC, 0x3CCF, 0x3CF0, 0x3CF3, 0x3CFC, 0x3CFF, 
+  0x3F00, 0x3F03, 0x3F0C, 0x3F0F, 0x3F30, 0x3F33, 0x3F3C, 0x3F3F, 0x3FC0, 0x3FC3, 0x3FCC, 0x3FCF, 0x3FF0, 0x3FF3, 0x3FFC, 0x3FFF, 
+  0xC000, 0xC003, 0xC00C, 0xC00F, 0xC030, 0xC033, 0xC03C, 0xC03F, 0xC0C0, 0xC0C3, 0xC0CC, 0xC0CF, 0xC0F0, 0xC0F3, 0xC0FC, 0xC0FF, 
+  0xC300, 0xC303, 0xC30C, 0xC30F, 0xC330, 0xC333, 0xC33C, 0xC33F, 0xC3C0, 0xC3C3, 0xC3CC, 0xC3CF, 0xC3F0, 0xC3F3, 0xC3FC, 0xC3FF, 
+  0xCC00, 0xCC03, 0xCC0C, 0xCC0F, 0xCC30, 0xCC33, 0xCC3C, 0xCC3F, 0xCCC0, 0xCCC3, 0xCCCC, 0xCCCF, 0xCCF0, 0xCCF3, 0xCCFC, 0xCCFF, 
+  0xCF00, 0xCF03, 0xCF0C, 0xCF0F, 0xCF30, 0xCF33, 0xCF3C, 0xCF3F, 0xCFC0, 0xCFC3, 0xCFCC, 0xCFCF, 0xCFF0, 0xCFF3, 0xCFFC, 0xCFFF, 
+  0xF000, 0xF003, 0xF00C, 0xF00F, 0xF030, 0xF033, 0xF03C, 0xF03F, 0xF0C0, 0xF0C3, 0xF0CC, 0xF0CF, 0xF0F0, 0xF0F3, 0xF0FC, 0xF0FF, 
+  0xF300, 0xF303, 0xF30C, 0xF30F, 0xF330, 0xF333, 0xF33C, 0xF33F, 0xF3C0, 0xF3C3, 0xF3CC, 0xF3CF, 0xF3F0, 0xF3F3, 0xF3FC, 0xF3FF, 
+  0xFC00, 0xFC03, 0xFC0C, 0xFC0F, 0xFC30, 0xFC33, 0xFC3C, 0xFC3F, 0xFCC0, 0xFCC3, 0xFCCC, 0xFCCF, 0xFCF0, 0xFCF3, 0xFCFC, 0xFCFF, 
+  0xFF00, 0xFF03, 0xFF0C, 0xFF0F, 0xFF30, 0xFF33, 0xFF3C, 0xFF3F, 0xFFC0, 0xFFC3, 0xFFCC, 0xFFCF, 0xFFF0, 0xFFF3, 0xFFFC, 0xFFFF
+};
+
+constexpr uint8_t gcvLowResFontData[80] = {
+  0xF0, 0x90, 0x90, 0x90, 0xF0,
+  0x20, 0x60, 0x20, 0x20, 0x70,
+  0xF0, 0x10, 0xF0, 0x80, 0xF0,
+  0xF0, 0x10, 0xF0, 0x10, 0xF0,
+  0x90, 0x90, 0xF0, 0x10, 0x10,
+  0xF0, 0x80, 0xF0, 0x10, 0xF0,
+  0xF0, 0x80, 0xF0, 0x90, 0xF0,
+  0xF0, 0x10, 0x20, 0x40, 0x40,
+  0xF0, 0x90, 0xF0, 0x90, 0xF0,
+  0xF0, 0x90, 0xF0, 0x10, 0xF0,
+  0xF0, 0x90, 0xF0, 0x90, 0x90,
+  0xE0, 0x90, 0xE0, 0x90, 0xE0,
+  0xF0, 0x80, 0x80, 0x80, 0xF0,
+  0xE0, 0x90, 0x90, 0x90, 0xE0,
+  0xF0, 0x80, 0xF0, 0x80, 0xF0,
+  0xF0, 0x80, 0xF0, 0x80, 0x80
+};
+
 Interpreter::Interpreter(unsigned ticksPerSecond, Display &display, Buzzer &buzzer, Keypad &keypad):
   mvMemory(scMemorySize),
   mCallStack{},
@@ -12,7 +50,13 @@ Interpreter::Interpreter(unsigned ticksPerSecond, Display &display, Buzzer &buzz
   mrKeypad{keypad},
   mcTicksPerSecond{ticksPerSecond},
   mvSpecialReg{},
-  mvReg{} {}
+  mvReg{},
+  mIsHighResMode{false} {
+  // Font sprite data goes into the interpreter reserved memory area
+  memcpy(mvMemory.data() + scLowRestFontAddr, gcvLowResFontData, sizeof(gcvLowResFontData));
+  // Initialize any non-zero registers at startup
+  mvSpecialReg[SR_PC] = scResetVector;
+}
 
 void Interpreter::tick() {
   // decodes all possible machine code arithmetic opcodes
@@ -28,9 +72,9 @@ void Interpreter::tick() {
   unsigned inst = (mvMemory[pc] << 8) | mvMemory[pc + 1];
 
   // extract fields
-  unsigned regDst  = (inst & 0x0F00) >> 8; // destination register index
-  unsigned regSrc  = (inst & 0x00F0) >> 4; // source register index
-  unsigned opcode  = (inst & 0x000F);      // arithmetic opcode
+  unsigned iRegDst = (inst & 0x0F00) >> 8; // destination register index
+  unsigned iRegSrc = (inst & 0x00F0) >> 4; // source register index
+  unsigned opcode  = (inst & 0x000F);      // arithmetic opcode or sprite index
   unsigned imm8    = (inst & 0x00FF);      // 8-bit immediate
   unsigned imm12   = (inst & 0x0FFF);      // 12-bit immediate
 
@@ -59,25 +103,25 @@ void Interpreter::tick() {
     mvSpecialReg[SR_PC] = imm12;
     break;
   case 0x3000: // 3XNN - skip if equal immediate
-    executeArithmetic(Opcode::JEQ, regDst, imm8);
+    executeArithmetic(Opcode::JEQ, iRegDst, imm8);
     break;
   case 0x4000: // 4XNN - skip if nonequal immediate
-    executeArithmetic(Opcode::JNEQ, regDst, imm8);
+    executeArithmetic(Opcode::JNEQ, iRegDst, imm8);
     break;
   case 0x5000: // 5XY0 - skip if equal
-    executeArithmetic(Opcode::JEQ, regDst, mvReg[regSrc]);
+    executeArithmetic(Opcode::JEQ, iRegDst, mvReg[iRegSrc]);
     break;
   case 0x6000: // 6XNN - load immediate
-    executeArithmetic(Opcode::SET, regDst, imm8);
+    executeArithmetic(Opcode::SET, iRegDst, imm8);
     break;
   case 0x7000: // 7XNN - increment
-    executeArithmetic(Opcode::ADD, regDst, imm8);
+    executeArithmetic(Opcode::ADD, iRegDst, imm8);
     break;
   case 0x8000: // 8XNN - general arithmetic
-    executeArithmetic(opcodeMap[opcode], regDst, mvReg[regSrc]); 
+    executeArithmetic(opcodeMap[opcode], iRegDst, mvReg[iRegSrc]); 
     break;
   case 0x9000: // 9XY0 - skip if nonequal
-    executeArithmetic(Opcode::JNEQ, regDst, mvReg[regSrc]);
+    executeArithmetic(Opcode::JNEQ, iRegDst, mvReg[iRegSrc]);
     break;
   case 0xA000: // ANNN - load I
     mvSpecialReg[SR_I] = imm12;
@@ -86,9 +130,10 @@ void Interpreter::tick() {
     mvSpecialReg[SR_I] = mvReg[R_V0] + imm12;
     break;
   case 0xC000: // CXNN - load random
-    executeArithmetic(Opcode::RAND, regDst, imm8);
+    executeArithmetic(Opcode::RAND, iRegDst, imm8);
     break;
   case 0xD000: // DXYN - draw
+    executeDraw(mvReg[iRegDst], mvReg[iRegSrc], opcode);
     break;
   case 0xE000: // EX9E, EXA1 - keypad access
     break;
@@ -111,11 +156,11 @@ void Interpreter::tick() {
   }
 }
 
-void Interpreter::loadProgram(size_t where, char const* data, size_t count) {
+void Interpreter::loadProgram(char const* data, size_t count, size_t where) {
   if(where + count > scMemorySize) {
     throw std::out_of_range("program exceeds memory bounds or capacity");
   }
-  memcpy(mvMemory.data(), data, count);
+  memcpy(mvMemory.data() + where, data, count);
 }
 
 void Interpreter::executeArithmetic(Opcode opcode, int iReg, reg_t operand) {
@@ -165,4 +210,60 @@ void Interpreter::executeArithmetic(Opcode opcode, int iReg, reg_t operand) {
   }
 }
 
+void Interpreter::executeDraw(uint8_t x, uint8_t y, uint8_t n) { 
+  size_t iMemAddr = mvSpecialReg[SR_I]; // address of the sprite data in memory
+  int collisionCount = 0; // number of scanlines in which any pixel changes from on to off
+
+  // coordinates are doubled in low resolution mode
+  if(!mIsHighResMode) {
+    x *= 2;
+    y *= 2;
+  }
+  x %= gcWidth;
+  y %= gcHeight;
+  // make x=0 be the right side of the screen instead of the left
+  x = gcWidth - x;
+
+  // draw each row of the sprite
+  for(int i = 0; i < (mIsHighResMode && n == 0 ? 16 : n); i++) {
+    uint16_t spriteRowBits;
+    if(mIsHighResMode) {
+      // draws an 8xN sprite
+      spriteRowBits = mvMemory[iMemAddr++] << 8;
+      if(n == 0) {
+        // draws an 16xN sprite, so fetch another byte from sprite data
+        spriteRowBits |= mvMemory[iMemAddr++];
+      }
+    } else {
+      // in low-res mode, each sprite pixel draws two on-screen pixels
+      spriteRowBits = gcvLowResToHighResRowLookupTable[mvMemory[iMemAddr++]];
+    }
+
+    // convert to bitset and shift into absolute horizontal position on the screen
+    Scanline spriteScanline(spriteRowBits);
+    if(x < 16) {
+      spriteScanline >>= (16 - x);
+    } else {
+      spriteScanline <<= (x - 16);
+    }
+
+    // we draw one scanline per sprite row in high-res mode, but twice in low-res mode
+    for(int j = 0; j < (mIsHighResMode ? 1 : 2); j++) {
+      Scanline &targetScanline = mrDisplay.mpFramebuffer->at(y + i * (mIsHighResMode ? 1 : 2) + j);
+      if((targetScanline & spriteScanline) != 0) {
+        collisionCount += 1;
+      }
+      // blit the sprite bitset into the screen
+      targetScanline ^= spriteScanline;
+    }
+
+    // update state flags
+    if(mIsHighResMode) {
+      mvReg[R_VF] = collisionCount;  
+    } else {
+      mvReg[R_VF] = (collisionCount > 0 ? 1 : 0);
+    }
+  }
+}
+
 }; // namespace chochochip8 
diff --git a/Interpreter.hpp b/Interpreter.hpp
index b88c15d..83c38d2 100644
--- a/Interpreter.hpp
+++ b/Interpreter.hpp
@@ -14,6 +14,7 @@ private:
   using sreg_t = unsigned;
 
 public:
+  constexpr static sreg_t scLowRestFontAddr = 0x0000;
   constexpr static sreg_t scResetVector = 0x0200;
   constexpr static size_t scMemorySize = 4096;
 
@@ -35,10 +36,11 @@ public:
 public:
   Interpreter(unsigned ticksPerSecond, Display &display, Buzzer &buzzer, Keypad &keypad);
   void tick();
-  void loadProgram(size_t where, char const* data, size_t count);
+  void loadProgram(char const* data, size_t count, size_t where = scResetVector);
 
 private:
   void executeArithmetic(Opcode opcode, int iReg, reg_t operand);
+  void executeDraw(uint8_t x, uint8_t y, uint8_t n);
 
 private:
   std::vector<uint8_t> mvMemory;
@@ -49,6 +51,7 @@ private:
   const unsigned mcTicksPerSecond;
   sreg_t mvSpecialReg[SR_COUNT];
   reg_t mvReg[R_COUNT];
+  bool mIsHighResMode;
 }; // class Interpreter
 
 }; // namespace chocohip8
diff --git a/Peripherals.hpp b/Peripherals.hpp
index 7ed23a7..84b5ecb 100644
--- a/Peripherals.hpp
+++ b/Peripherals.hpp
@@ -37,7 +37,7 @@ namespace chocochip8 {
   class Keypad {
   public:
     virtual ~Keypad() = default;
-    virtual void isKeyPressed(Key key) = 0;
+    virtual bool isKeyPressed(Key key) = 0;
   };
 
 }; // namespace chocochip8
diff --git a/main.cpp b/main.cpp
index 2b1513b..d176cd3 100644
--- a/main.cpp
+++ b/main.cpp
@@ -3,6 +3,7 @@
 
 #include "BuzzerSDL.hpp"
 #include "DisplaySDL.hpp"
+#include "Interpreter.hpp"
 #include "Peripherals.hpp"
 
 int main(int argc, char* args[]) {
@@ -11,18 +12,38 @@ int main(int argc, char* args[]) {
     return 1;
   }
 
-  class DisplayTest : public DisplaySDL {
-  public:
-    DisplayTest() : DisplaySDL(1280, 640, 0xff0000, 0x00ff00) {
-      for(int i = 0; i < chocochip8::gcHeight; i+=2) {
-        mpFramebuffer->at(i).set();
-      }
-    }
+  class TestKeypad : public chocochip8::Keypad {
+    bool isKeyPressed(chocochip8::Key) override { return false; }
   };
 
   BuzzerSDL buzzer(440);
-  //buzzer.on();
-  DisplayTest display;
+  DisplaySDL display(1280, 640);
+  TestKeypad keypad;
+  chocochip8::Interpreter chip8(90, display, buzzer, keypad);
+
+  uint8_t prog[] = {
+    0xA0, 0x00,  // LD I,0
+    0x60, 0x00,  // LD $0,0
+    0x61, 0x00,  // LD $1,0
+    0xD0, 0x15,  // DRW $0, $1, 5
+    0xA0, 0x05,  // LD I,5
+    0x60, 0x3C,  // LD $0,60
+    0x61, 0x00,  // LD $1,0
+    0xD0, 0x15,  // DRW $0, $1, 5
+    0xA0, 0x0A,  // LD I,10
+    0x60, 0x00,  // LD $0,0
+    0x61, 0x1B,  // LD $1,27
+    0xD0, 0x15,  // DRW $0, $1, 5
+    0xA0, 0x0F,  // LD I,15
+    0x60, 0x3C,  // LD $0,60
+    0x61, 0x1B,  // LD $1,27
+    0xD0, 0x15,  // DRW $0, $1, 5
+  };
+
+  chip8.loadProgram((char*)prog, sizeof(prog));
+  for(int i = 0; i < sizeof(prog) / 2; i++) {
+    chip8.tick();
+  }
 
   SDL_Event event;
   while(SDL_WaitEvent(&event) && event.type != SDL_QUIT) {