diff --git a/cli/CMakeLists.txt b/cli/CMakeLists.txt
index b80293f..ccbf053 100644
--- a/cli/CMakeLists.txt
+++ b/cli/CMakeLists.txt
@@ -20,6 +20,7 @@ add_executable(gb6
     ../src/instructions.c
     ../src/lcd.c
     ../src/rom.c
+    ../src/mbc.c
     emulator.c
     lcd_imgui.c
     imgui/imgui_demo.cpp
diff --git a/src/cpu.c b/src/cpu.c
index 7f3ffbf..fff4b21 100644
--- a/src/cpu.c
+++ b/src/cpu.c
@@ -453,6 +453,34 @@ static void conditional_jump(struct cpu *cpu, u8 opc, u8 neg_op, int flag) {
     }
 }
 
+static void daa(struct cpu *cpu)
+{
+    // https://forums.nesdev.org/viewtopic.php?t=15944
+    if (!flag_isset(cpu, FLAG_SIGN)) {
+        if (flag_isset(cpu, FLAG_CARRY) || cpu->a > 0x99) {
+            cpu->a += 0x60;
+            set_flag(cpu, FLAG_CARRY);
+        }
+        if (flag_isset(cpu, FLAG_HALF_CARRY) || (cpu->a & 0x0f) > 0x09) {
+            cpu->a += 0x6;
+        }
+    } else {
+        if (flag_isset(cpu, FLAG_CARRY)) {
+            cpu->a -= 0x60;
+        }
+        if (flag_isset(cpu, FLAG_HALF_CARRY)) {
+            cpu->a -= 0x6;
+        }
+    }
+
+    if (cpu->a) {
+        set_flag(cpu, FLAG_ZERO);
+    } else {
+        clear_flag(cpu, FLAG_ZERO);
+    }
+    clear_flag(cpu, FLAG_HALF_CARRY);
+}
+
 static u16 handlers[] = { 0x40, 0x48, 0x50, 0x58, 0x60 };
 
 static u16 check_interrupts(struct cpu *cpu)
@@ -480,6 +508,9 @@ static u16 check_interrupts(struct cpu *cpu)
     return 0;
 }
 
+/*
+*/
+
 void cpu_step(struct cpu *cpu)
 {
     u8 temp;
@@ -512,6 +543,9 @@ void cpu_step(struct cpu *cpu)
         case 0x0f: // RRCA
             cpu->a = rrc(cpu, cpu->a);
             break;
+        case 0x10: // STOP
+            cpu->pc++;
+            break;
         case 0x11: // LD DE,d16
             write_de(cpu, read16(cpu, cpu->pc));
             cpu->pc += 2;
@@ -892,6 +926,7 @@ void cpu_step(struct cpu *cpu)
         case 0xff: push(cpu, cpu->pc); cpu->pc = 0x38; break;
 
         case 0x27: // DAA
+            daa(cpu);
             break;
 
         case 0x76: // HALT
diff --git a/src/dmg.c b/src/dmg.c
index 4541208..0fde300 100644
--- a/src/dmg.c
+++ b/src/dmg.c
@@ -5,6 +5,7 @@
 #include "rom.h"
 #include "lcd.h"
 #include "dmg.h"
+#include "mbc.h"
 #include "types.h"
 #include "bootstrap.h"
 
@@ -54,6 +55,12 @@ static int counter;
 u8 dmg_read(void *_dmg, u16 address)
 {
     struct dmg *dmg = (struct dmg *) _dmg;
+    u8 mbc_data;
+
+    if (mbc_read(dmg->rom->mbc, dmg, address, &mbc_data)) {
+        return mbc_data;
+    }
+
 //    if (address < 0x100) {
 //        return dmg_boot_rom[address];
 //    } else if (address < 0x4000) {
@@ -93,6 +100,11 @@ u8 dmg_read(void *_dmg, u16 address)
 void dmg_write(void *_dmg, u16 address, u8 data)
 {
     struct dmg *dmg = (struct dmg *) _dmg;
+
+    if (mbc_write(dmg->rom->mbc, dmg, address, data)) {
+        return;
+    }
+
     if (address < 0x4000) {
         printf("warning: writing 0x%04x in rom\n", address);
     } else if (address < 0x8000) {
diff --git a/src/dmg.h b/src/dmg.h
index 2ae02b0..3419fd9 100644
--- a/src/dmg.h
+++ b/src/dmg.h
@@ -1,9 +1,7 @@
 #ifndef _DMG_H
 #define _DMG_H
 
-#include "cpu.h"
-#include "rom.h"
-#include "lcd.h"
+#include "types.h"
 
 #define FIELD_JOY 1
 #define FIELD_ACTION 2
@@ -17,6 +15,10 @@
 #define BUTTON_SELECT (1 << 2)
 #define BUTTON_START (1 << 3)
 
+struct cpu;
+struct rom;
+struct lcd;
+
 struct dmg {
     struct cpu *cpu;
     struct rom *rom;
diff --git a/src/mbc.c b/src/mbc.c
new file mode 100644
index 0000000..2601820
--- /dev/null
+++ b/src/mbc.c
@@ -0,0 +1,91 @@
+#include <stdlib.h>
+#include <stdio.h>
+
+#include "types.h"
+#include "mbc.h"
+#include "dmg.h"
+#include "rom.h"
+
+static int mbc_noop_read(struct mbc *mbc, struct dmg *dmg, u16 addr, u8 *out_data)
+{
+  return 0;
+}
+
+static int mbc_noop_write(struct mbc *mbc, struct dmg *dmg, u16 addr, u8 data)
+{
+  return 0;
+}
+
+static int mbc1_read(struct mbc *mbc, struct dmg *dmg, u16 addr, u8 *out_data)
+{
+  if (addr >= 0x4000 && addr <= 0x7fff) {
+    int use_bank = mbc->rom_bank || 1;
+    *out_data = dmg->rom->data[0x4000 * use_bank + (addr & 0x3fff)];
+    return 1;
+  } else if (addr >= 0xa000 && addr <= 0xbfff) {
+    if (mbc->ram_enabled) {
+      *out_data = mbc->ram[0x2000 * mbc->ram_bank + (addr & 0x1fff)];
+    } else {
+      *out_data = 0xff;
+    }
+    return 1;
+  }
+
+  return 0;
+}
+
+static int mbc1_write(struct mbc *mbc, struct dmg *dmg, u16 addr, u8 data)
+{
+  if (addr >= 0 && addr <= 0x1fff) {
+    mbc->ram_enabled = (data & 0xf) == 0xa;
+    return 1;
+  } else if (addr >= 0x2000 && addr <= 0x3fff) {
+    mbc->rom_bank = data & 0x1f;
+    return 1;
+  } else if (addr >= 0x4000 && addr <= 0x5fff) {
+    mbc->ram_bank = data & 0x03;
+    return 1;
+  } else if (addr >= 0x6000 && addr <= 0x7fff) {
+    //printf("sel %d\n", data);
+    return 1;
+  } else if (addr >= 0xa000 && addr <= 0xbfff) {
+    if (mbc->ram_enabled) {
+      mbc->ram[0x2000 * mbc->ram_bank + (addr & 0x1fff)] = data;
+      return 1;
+    }
+  }
+  return 0;
+}
+
+struct mbc mbc_noop = {
+  mbc_noop_read,
+  mbc_noop_write,
+};
+
+struct mbc mbc1 = {
+  mbc1_read,
+  mbc1_write,
+};
+
+struct mbc *mbc_new(int type)
+{
+  switch (type) {
+    case 0:
+      return &mbc_noop;
+    case 1:
+    case 2:
+    case 3:
+      return &mbc1;
+  }
+  return NULL;
+}
+
+int mbc_read(struct mbc *mbc, struct dmg *dmg, u16 addr, u8 *out_data)
+{
+  return mbc->read_fn(mbc, dmg, addr, out_data);
+}
+
+int mbc_write(struct mbc *mbc, struct dmg *dmg, u16 addr, u8 data)
+{
+  return mbc->write_fn(mbc, dmg, addr, data);
+}
diff --git a/src/mbc.h b/src/mbc.h
new file mode 100644
index 0000000..d1d429b
--- /dev/null
+++ b/src/mbc.h
@@ -0,0 +1,22 @@
+#ifndef _MBC_H
+#define _MBC_H
+
+#include "types.h"
+
+struct dmg;
+
+struct mbc {
+  int (*read_fn)(struct mbc *, struct dmg *, u16, u8 *);
+  int (*write_fn)(struct mbc *, struct dmg *, u16, u8);
+  int type;
+  int rom_bank;
+  int ram_bank;
+  int ram_enabled;
+  u8 ram[0x8000];
+};
+
+struct mbc *mbc_new(int type);
+int mbc_read(struct mbc *mbc, struct dmg *dmg, u16 addr, u8 *out_data);
+int mbc_write(struct mbc *mbc, struct dmg *dmg, u16 addr, u8 data);
+
+#endif
\ No newline at end of file
diff --git a/src/rom.c b/src/rom.c
index 86b4349..f3d1130 100644
--- a/src/rom.c
+++ b/src/rom.c
@@ -17,12 +17,15 @@ int rom_load(struct rom *rom, const char *filename)
     len = ftell(fp);
     rewind(fp);
 
-    rom->type = 0; // TODO read type from cart
     rom->data = malloc(len);
     rom->length = len;
     if (fread(rom->data, 1, len, fp) < len) {
         return 0;
     }
+    rom->mbc = mbc_new(rom->data[0x147]);
+    if (!rom->mbc) {
+        return 0;
+    }
 
     return 1;
 }
diff --git a/src/rom.h b/src/rom.h
index 4bcb1f5..a0bf7b5 100644
--- a/src/rom.h
+++ b/src/rom.h
@@ -2,11 +2,12 @@
 #define _ROM_H
 
 #include "types.h"
+#include "mbc.h"
 
 struct rom {
     u32 length;
-    int type;
     u8 *data;
+    struct mbc *mbc;
 };
 
 int rom_load(struct rom *rom, const char *filename);