const unsigned char code loot[256] = {0x31,0x32,0x33,0x00,0x34,0x35, // etc};
// here 0x00 is used as a marker for not possible conditions

// inside ISR
{
   unsigned char x; 
   x = XBYTE[0x0a000]; 
   if ((x = loot[x]) != 0x00)
   {
      P1 = x;
      2LCD();
   }
}