diff --git a/terminal/master/src/main.cpp b/terminal/master/src/main.cpp
index 907bf6d..a3e62c8 100644
--- a/terminal/master/src/main.cpp
+++ b/terminal/master/src/main.cpp
@@ -5,15 +5,18 @@ void resetPuzzles();
 
 /* ========================================================= */
 const uint8_t ARCHIV_ADDR = 0x10;
-const uint8_t CMD_POWER_OFF = 0x01;
-const uint8_t CMD_LIGHT_INDEX = 0x02;
-const uint8_t CMD_DRAWER_INDEX = 0x03;
+
+const uint8_t BITMASK_CMD = 0b00011000;
+const uint8_t BITMASK_PAYLOAD = 0b00000111;
+
+const uint8_t CMD_POWER_OFF    = 0b00001000;
+const uint8_t CMD_LIGHT_INDEX  = 0b00010000;
+const uint8_t CMD_DRAWER_INDEX = 0b00011000;
 
 void setDrawerLight(uint8_t index)
 {
   Wire.beginTransmission(ARCHIV_ADDR);
-  Wire.write(CMD_LIGHT_INDEX);
-  Wire.write(index);
+  Wire.write(CMD_LIGHT_INDEX | (index & BITMASK_PAYLOAD));
   Wire.endTransmission();
 }
 
@@ -27,8 +30,7 @@ void turnLightsOff()
 void openDrawer(uint8_t index)
 {
   Wire.beginTransmission(ARCHIV_ADDR);
-  Wire.write(CMD_DRAWER_INDEX);
-  Wire.write(index);
+  Wire.write(CMD_DRAWER_INDEX | (index & BITMASK_PAYLOAD));
   Wire.endTransmission();
 }
 /* ========================================================= */