diff --git a/stk500v2/command.hpp b/stk500v2/command.hpp
new file mode 100644
index 0000000..68742a1
--- /dev/null
+++ b/stk500v2/command.hpp
@@ -0,0 +1,113 @@
+#pragma once
+
+#include <stdint.h>
+
+//////////////////////////////////////////////////////////////////////////
+// STK message constants
+
+static constexpr uint8_t MESSAGE_START = 0x1B; // ASCII ESC
+static constexpr uint8_t TOKEN = 0x0E;
+
+//////////////////////////////////////////////////////////////////////////
+// STK general command constants
+
+static constexpr uint8_t CMD_SIGN_ON = 0x01;
+static constexpr uint8_t CMD_SET_PARAMETER = 0x02;
+static constexpr uint8_t CMD_GET_PARAMETER = 0x03;
+static constexpr uint8_t CMD_SET_DEVICE_PARAMETERS = 0x04;
+static constexpr uint8_t CMD_OSCCAL = 0x05;
+static constexpr uint8_t CMD_LOAD_ADDRESS = 0x06;
+static constexpr uint8_t CMD_FIRMWARE_UPGRADE = 0x07;
+
+//////////////////////////////////////////////////////////////////////////
+// STK ISP command constants
+
+static constexpr uint8_t CMD_ENTER_PROGMODE_ISP = 0x10;
+static constexpr uint8_t CMD_LEAVE_PROGMODE_ISP = 0x11;
+static constexpr uint8_t CMD_CHIP_ERASE_ISP = 0x12;
+static constexpr uint8_t CMD_PROGRAM_FLASH_ISP = 0x13;
+static constexpr uint8_t CMD_READ_FLASH_ISP = 0x14;
+static constexpr uint8_t CMD_PROGRAM_EEPROM_ISP = 0x15;
+static constexpr uint8_t CMD_READ_EEPROM_ISP = 0x16;
+static constexpr uint8_t CMD_PROGRAM_FUSE_ISP = 0x17;
+static constexpr uint8_t CMD_READ_FUSE_ISP = 0x18;
+static constexpr uint8_t CMD_PROGRAM_LOCK_ISP = 0x19;
+static constexpr uint8_t CMD_READ_LOCK_ISP = 0x1A;
+static constexpr uint8_t CMD_READ_SIGNATURE_ISP = 0x1B;
+static constexpr uint8_t CMD_READ_OSCCAL_ISP = 0x1C;
+static constexpr uint8_t CMD_SPI_MULTI = 0x1D;
+
+//////////////////////////////////////////////////////////////////////////
+// STK PP command constants
+
+static constexpr uint8_t CMD_ENTER_PROGMODE_PP = 0x20;
+static constexpr uint8_t CMD_LEAVE_PROGMODE_PP = 0x21;
+static constexpr uint8_t CMD_CHIP_ERASE_PP = 0x22;
+static constexpr uint8_t CMD_PROGRAM_FLASH_PP = 0x23;
+static constexpr uint8_t CMD_READ_FLASH_PP = 0x24;
+static constexpr uint8_t CMD_PROGRAM_EEPROM_PP = 0x25;
+static constexpr uint8_t CMD_READ_EEPROM_PP = 0x26;
+static constexpr uint8_t CMD_PROGRAM_FUSE_PP = 0x27;
+static constexpr uint8_t CMD_READ_FUSE_PP = 0x28;
+static constexpr uint8_t CMD_PROGRAM_LOCK_PP = 0x29;
+static constexpr uint8_t CMD_READ_LOCK_PP = 0x2A;
+static constexpr uint8_t CMD_READ_SIGNATURE_PP = 0x2B;
+static constexpr uint8_t CMD_READ_OSCCAL_PP = 0x2C;
+
+static constexpr uint8_t CMD_SET_CONTROL_STACK = 0x2D;
+
+//////////////////////////////////////////////////////////////////////////
+// STK HVSP command constants
+
+static constexpr uint8_t CMD_ENTER_PROGMODE_HVSP = 0x30;
+static constexpr uint8_t CMD_LEAVE_PROGMODE_HVSP = 0x31;
+static constexpr uint8_t CMD_CHIP_ERASE_HVSP = 0x32;
+static constexpr uint8_t CMD_PROGRAM_FLASH_HVSP = 0x33;
+static constexpr uint8_t CMD_READ_FLASH_HVSP = 0x34;
+static constexpr uint8_t CMD_PROGRAM_EEPROM_HVSP = 0x35;
+static constexpr uint8_t CMD_READ_EEPROM_HVSP = 0x36;
+static constexpr uint8_t CMD_PROGRAM_FUSE_HVSP = 0x37;
+static constexpr uint8_t CMD_READ_FUSE_HVSP = 0x38;
+static constexpr uint8_t CMD_PROGRAM_LOCK_HVSP = 0x39;
+static constexpr uint8_t CMD_READ_LOCK_HVSP = 0x3A;
+static constexpr uint8_t CMD_READ_SIGNATURE_HVSP = 0x3B;
+static constexpr uint8_t CMD_READ_OSCCAL_HVSP = 0x3C;
+
+//////////////////////////////////////////////////////////////////////////
+// STK status constants
+
+// Success
+static constexpr uint8_t STATUS_CMD_OK = 0x00;
+
+// Warnings
+static constexpr uint8_t STATUS_CMD_TOUT = 0x80;
+static constexpr uint8_t STATUS_RDY_BSY_TOUT = 0x81;
+static constexpr uint8_t STATUS_SET_PARAM_MISSING = 0x82;
+
+// Errors
+static constexpr uint8_t STATUS_CMD_FAILED = 0xC0;
+static constexpr uint8_t STATUS_CKSUM_ERROR = 0xC1;
+static constexpr uint8_t STATUS_CMD_UNKNOWN = 0xC9;
+
+//////////////////////////////////////////////////////////////////////////
+// STK parameter constants
+static constexpr uint8_t PARAM_BUILD_NUMBER_LOW = 0x80;
+static constexpr uint8_t PARAM_BUILD_NUMBER_HIGH = 0x81;
+static constexpr uint8_t PARAM_HW_VER = 0x90;
+static constexpr uint8_t PARAM_SW_MAJOR = 0x91;
+static constexpr uint8_t PARAM_SW_MINOR = 0x92;
+static constexpr uint8_t PARAM_VTARGET = 0x94;
+static constexpr uint8_t PARAM_VADJUST = 0x95;
+static constexpr uint8_t PARAM_OSC_PSCALE = 0x96;
+static constexpr uint8_t PARAM_OSC_CMATCH = 0x97;
+static constexpr uint8_t PARAM_SCK_DURATION = 0x98;
+static constexpr uint8_t PARAM_TOPCARD_DETECT = 0x9A;
+static constexpr uint8_t PARAM_STATUS = 0x9C;
+static constexpr uint8_t PARAM_DATA = 0x9D;
+static constexpr uint8_t PARAM_RESET_POLARITY = 0x9E;
+static constexpr uint8_t PARAM_CONTROLLER_INIT = 0x9F;
+
+//////////////////////////////////////////////////////////////////////////
+// STK answer constants
+
+static constexpr uint8_t ANSWER_CKSUM_ERROR = 0xB0;
diff --git a/stk500v2/main.cpp b/stk500v2/main.cpp
index f0552a4..65eebe2 100644
--- a/stk500v2/main.cpp
+++ b/stk500v2/main.cpp
@@ -2,6 +2,8 @@
 
 #include "uart/uart.hpp"
 
+#include "command.hpp"
+
 using uart_interface = uart::Hardware0<uart::Config<115200>, uart::Driven::BLOCKING>;
 
 int main()
diff --git a/stk500v2/stk500v2.cppproj b/stk500v2/stk500v2.cppproj
index 6c553f9..f1fc821 100644
--- a/stk500v2/stk500v2.cppproj
+++ b/stk500v2/stk500v2.cppproj
@@ -215,6 +215,9 @@
     <Compile Include="clock.hpp">
       <SubType>compile</SubType>
     </Compile>
+    <Compile Include="command.hpp">
+      <SubType>compile</SubType>
+    </Compile>
     <Compile Include="flash\flash.hpp">
       <SubType>compile</SubType>
     </Compile>