Attempt to address Bernhard's comments

Refactor configuration to try to make items clearer (what defines a
panel vs what is user changeable).

Marlin/Configuration.h

  #define NEWPANEL
 #endif 
 
-// I2C PANELS
+//I2C PANELS
 
 //#define LCD_I2C_SAINSMART_YWROBOT
 #ifdef LCD_I2C_SAINSMART_YWROBOT
   // This uses the LiquidCrystal_I2C library ( https://bitbucket.org/fmalpartida/new-liquidcrystal/wiki/Home )
   // Make sure it is placed in the Arduino libraries directory.
   #define LCD_I2C_TYPE_PCF8575
-  #define LCD_I2C
-  #define ULTIPANEL
-  #define NEWPANEL
   #define LCD_I2C_ADDRESS 0x27   // I2C Address of the port expander
+  #define NEWPANEL
+  #define ULTIPANEL 
 #endif
 
-// PANELOLU2 LCD with status LEDs, separate encoder and click inputs
+//PANELOLU2 LCD with status LEDs, separate encoder and click inputs
 //#define LCD_I2C_PANELOLU2
 #ifdef LCD_I2C_PANELOLU2
   // This uses the LiquidTWI2 library ( https://github.com/lincomatic/LiquidTWI2 ).
   // Make sure it is placed in the Arduino libraries directory.
   #define LCD_I2C_TYPE_MCP23017
-  #define LCD_I2C
-  #define ULTIPANEL
+  #define LCD_I2C_ADDRESS 0x20 // I2C Address of the port expander
+  #define LCD_USE_I2C_BUZZER //comment out to disable buzzer on LCD
   #define NEWPANEL
-  #define LCD_I2C_ADDRESS 0x20
-  #define LCD_HAS_I2C_BUZZ //comment out to disable buzzer on LCD
-  #define LCD_HAS_STATUS_INDICATORS  
+  #define ULTIPANEL 
 #endif
 
-// VIKI LCD with status LEDs, integrated click & L/R/U/P buttons, separate encoder inputs
+//VIKI LCD with status LEDs, integrated click & L/R/U/P buttons, separate encoder inputs
 //#define LCD_I2C_VIKI
 #ifdef LCD_I2C_VIKI
   // This uses the LiquidTWI2 library (https://github.com/lincomatic/LiquidTWI2).
   // Make sure it is placed in the Arduino libraries directory.
-  #define LCD_I2C_TYPE_MCP23017
-  #define LCD_I2C
-  #define ULTIPANEL
+  #define LCD_I2C_TYPE_MCP23017 
+  #define LCD_I2C_ADDRESS 0x20 // I2C Address of the port expander
   #define NEWPANEL
-  #define LCD_I2C_ADDRESS 0x20
-  #define LCD_HAS_STATUS_INDICATORS  
+  #define ULTIPANEL 
 #endif
 
 #ifdef ULTIPANEL

Marlin/Marlin.pde

 #include "pins.h"
 
 #ifdef ULTRA_LCD
-  #ifdef LCD_I2C
+  #if defined(LCD_I2C_TYPE_PCF8575)
     #include <Wire.h>
-    #if defined(LCD_I2C_TYPE_PCF8575)
-      #include <LiquidCrystal_I2C.h>
-    #elif defined(LCD_I2C_TYPE_MCP23017)
-      #ifdef LCD_I2C_PANELOLU2
-        #include <LiquidTWI2.h>
-        #ifndef PANELOLU2
-          #error You must uncomment #define PANELOLU2 in LiquidTWI2.h for LiquidTWI2.cpp to compile correctly
-        #endif
-      #else
-        #include <LiquidTWI2.h>
-      #endif
-    #else
-      #error Unknown I2C LCD type    
+    #include <LiquidCrystal_I2C.h>
+  #elif defined(LCD_I2C_TYPE_MCP23017) || defined(LCD_I2C_TYPE_MCP23008)
+    #include <Wire.h>
+    #include <LiquidTWI2.h>
+    #if defined(LCD_I2C_PANELOLU2) && !defined(PANELOLU2)
+      #error You must uncomment "#define PANELOLU2" in LiquidTWI2.h for LiquidTWI2.cpp to compile correctly
     #endif
   #else
     #include <LiquidCrystal.h>

Marlin/ultralcd.cpp

     lcd_oldcardstatus = IS_SD_INSERTED;
 #endif//(SDCARDDETECT > -1)
     lcd_buttons_update();
+#ifdef ULTIPANEL    
     encoderDiff = 0;
+#endif    
 }
 
 void lcd_update()
     
     lcd_buttons_update();
     
-    #ifdef LCD_HAS_EXTRA_BUTTONS
-    buttons |= lcd_read_extra_buttons(); // buttons which take too long to read in interrupt context
+    #ifdef LCD_HAS_SLOW_BUTTONS
+    buttons |= lcd_implementation_read_slow_buttons(); // buttons which take too long to read in interrupt context
     #endif
     
     #if (SDCARDDETECT > -1)
         if (LCD_CLICKED)
             timeoutToStatus = millis() + LCD_TIMEOUT_TO_STATUS;
 #endif//ULTIPANEL
-        
         (*currentMenu)();
+
+#ifdef LCD_HAS_STATUS_INDICATORS
+        lcd_implementation_update_indicators();
+#endif        
+        
 #ifdef ULTIPANEL
         if(timeoutToStatus < millis() && currentMenu != lcd_status_screen)
         {
     }
     lastEncoderBits = enc;
 }
-#endif//ULTIPANEL
 
 bool lcd_clicked() 
 { 
   return LCD_CLICKED;
 }
+#endif//ULTIPANEL
 
 /********************************/
 /** Float conversion utilities **/

Marlin/ultralcd_implementation_hitachi_HD44780.h

 * When selecting the rusian language, a slightly different LCD implementation is used to handle UTF8 characters.
 **/
 
-// Declare LCD class to use
-#if defined(LCD_I2C_TYPE_PCF8575)
-  // note: these are virtual pins on the PCF8575 controller not Arduino pins
-  #define LCD_I2C_PIN_BL  3
-  #define LCD_I2C_PIN_EN  2
-  #define LCD_I2C_PIN_RW  1
-  #define LCD_I2C_PIN_RS  0
-  #define LCD_I2C_PIN_D4  4
-  #define LCD_I2C_PIN_D5  5
-  #define LCD_I2C_PIN_D6  6
-  #define LCD_I2C_PIN_D7  7
-
-  #include <Wire.h>
-  #include <LCD.h>
-  #include <LiquidCrystal_I2C.h>
-  #define LCD_CLASS LiquidCrystal_I2C
-  LCD_CLASS lcd(LCD_I2C_ADDRESS,LCD_I2C_PIN_EN,LCD_I2C_PIN_RW,LCD_I2C_PIN_RS,LCD_I2C_PIN_D4,LCD_I2C_PIN_D5,LCD_I2C_PIN_D6,LCD_I2C_PIN_D7);
-#elif defined(LCD_I2C_TYPE_MCP23017)
-  //for the LED indicators (which maybe mapped to different things in lcd_implementation_update_indicators())
-  #define LED_A 0x04 //100
-  #define LED_B 0x02 //010
-  #define LED_C 0x01  //001
-
-  #include <Wire.h>
-  #include <LiquidTWI2.h>
-  #define LCD_CLASS LiquidTWI2
-  LCD_CLASS lcd(LCD_I2C_ADDRESS);  //An alternative I2C master address can be used in place of "0"
-#elif defined(LCD_I2C_TYPE_MCP23008)
-  #include <Wire.h>
-  #include <LiquidTWI2.h>
-  #define LCD_CLASS LiquidTWI2
-  LCD_CLASS lcd(LCD_I2C_ADDRESS);  //An alternative I2C master address can be used in place of "0"
-#else
-  #if LANGUAGE_CHOICE == 6
-    #include "LiquidCrystalRus.h"
-    #define LCD_CLASS LiquidCrystalRus
-  #else 
-    #include <LiquidCrystal.h>
-    #define LCD_CLASS LiquidCrystal
-  #endif  
-  LCD_CLASS lcd(LCD_PINS_RS, LCD_PINS_ENABLE, LCD_PINS_D4, LCD_PINS_D5,LCD_PINS_D6,LCD_PINS_D7);  //RS,Enable,D4,D5,D6,D7
-#endif
-
 extern volatile uint8_t buttons;  //the last checked buttons in a bit array.
 
-// provide default button bitmask and encoder definitions (note this is not pin or motherboard specific)
-#ifdef LCD_I2C_VIKI
-  //encoder rotation values
-  #define encrot0 0
-  #define encrot1 2
-  #define encrot2 3
-  #define encrot3 1
-
-  #define BLEN_C 2
-  #define BLEN_B 1
-  #define BLEN_A 0
-
-  #define EN_C (1<<BLEN_C) // The stop/pause/resume button comes through BTN_ENC pin (for consistency with NEWPANEL code)
-  #define EN_B (1<<BLEN_B) // The two encoder pins are connected through BTN_EN1 and BTN_EN2
-  #define EN_A (1<<BLEN_A)
-
-  #define B_I2C_BTN_OFFSET 3 // (the first three bit positions reserved for EN_A, EN_B, EN_C)
+////////////////////////////////////
+// Setup button and encode mappings for each panel (into 'buttons' variable)
+//
+// This is just to map common functions (across different panels) onto the same 
+// macro name. The mapping is independent of whether the button is directly connected or 
+// via a shift/i2c register.
+
+#ifdef ULTIPANEL
+// All Ultipanels might have an encoder - so this is always be mapped onto first two bits
+#define BLEN_B 1
+#define BLEN_A 0
+
+#define EN_B (1<<BLEN_B) // The two encoder pins are connected through BTN_EN1 and BTN_EN2
+#define EN_A (1<<BLEN_A)
+
+//
+// Setup other button mappings of each panel
+//
+#if defined(LCD_I2C_VIKI)
+  #define BLEN_C 2 // == pause/stop/restart button connected to BTN_ENC pin (named for consistency with NEWPANEL code)
+  #define EN_C (1<<BLEN_C) 
+
+  #define B_I2C_BTN_OFFSET (BLEN_C+1) // (the first three bit positions reserved for EN_A, EN_B, EN_C)
   
   // button and encoder bit positions within 'buttons'
-  #define B_ST (EN_C)                             // The pause/stop/resume button is mapped to EN_C for consistency with NEWPANEL 
-  #define B_LE (BUTTON_LEFT<<B_I2C_BTN_OFFSET)    // The remaining buttons are I2C read buttons.
+  #define B_ST (EN_C)                             // Map the pause/stop/resume button into its normalized functional name 
+  #define B_LE (BUTTON_LEFT<<B_I2C_BTN_OFFSET)    // The remaining normalized buttons are all read via I2C
   #define B_UP (BUTTON_UP<<B_I2C_BTN_OFFSET)
   #define B_MI (BUTTON_SELECT<<B_I2C_BTN_OFFSET)
   #define B_DW (BUTTON_DOWN<<B_I2C_BTN_OFFSET)
 
   #define LCD_CLICKED (buttons&(B_MI|B_RI|B_ST)) // pause/stop button also acts as click until we implement proper pause/stop.
 
-  // I2C buttons are likely to take too long to read inside interrupt context and so we read them during lcd_update
-  #define LCD_HAS_EXTRA_BUTTONS
-  
-#elif defined(NEWPANEL)
-  //from the same bit in the RAMPS Newpanel define
-  //encoder rotation values
-  #define encrot0 0
-  #define encrot1 2
-  #define encrot2 3
-  #define encrot3 1
- 
-  #define BLEN_C 2
-  #define BLEN_B 1
-  #define BLEN_A 0
+  // I2C buttons take too long to read inside an interrupt context and so we read them during lcd_update
+  #define LCD_HAS_SLOW_BUTTONS
 
+#elif defined(NEWPANEL)
+  // Standard Newpanel has just a single button (all direclty connected)
+  #define BLEN_C 2 // == select button
   #define EN_C (1<<BLEN_C)
-  #define EN_B (1<<BLEN_B)
-  #define EN_A (1<<BLEN_A)
-
   #define LCD_CLICKED (buttons&EN_C)
   
 #else // old style ULTIPANEL
-  //encoder rotation values
-  #ifndef ULTIMAKERCONTROLLER
-    #define encrot0 0
-    #define encrot1 2
-    #define encrot2 3
-    #define encrot3 1
-  #else
-    #define encrot0 0
-    #define encrot1 1
-    #define encrot2 3
-    #define encrot3 2
-  #endif
-
   //bits in the shift register that carry the buttons for:
   // left up center down right red(stop)
   #define BL_LE 7
   #define BL_RI 3
   #define BL_ST 2
 
-  #define BLEN_B 1
-  #define BLEN_A 0
-
   //automatic, do not change
   #define B_LE (1<<BL_LE)
   #define B_UP (1<<BL_UP)
   #define B_DW (1<<BL_DW)
   #define B_RI (1<<BL_RI)
   #define B_ST (1<<BL_ST)
-  #define EN_B (1<<BLEN_B)
-  #define EN_A (1<<BLEN_A)
   
   #define LCD_CLICKED (buttons&(B_MI|B_ST))
 #endif//else NEWPANEL
 
-#ifdef LCD_HAS_STATUS_INDICATORS  
-//forward declaration
-static void lcd_implementation_update_indicators();
+////////////////////////
+// Setup Rotary Encoder Bit Values (for two pin encoders to indicate movement)
+// These values are independent of which pins are used for EN_A and EN_B indications
+// The rotary encoder part is also independent to the chipset used for the LCD
+#if defined(EN_A) && defined(EN_B)
+  #ifndef ULTIMAKERCONTROLLER
+    #define encrot0 0
+    #define encrot1 2
+    #define encrot2 3
+    #define encrot3 1
+  #else
+    #define encrot0 0
+    #define encrot1 1
+    #define encrot2 3
+    #define encrot3 2
+  #endif
+#endif
+
+#endif //ULTIPANEL
+
+////////////////////////////////////
+// Create LCD class instance and chipset-specific information
+#if defined(LCD_I2C_TYPE_PCF8575)
+  // note: these are register mapped pins on the PCF8575 controller not Arduino pins
+  #define LCD_I2C_PIN_BL  3
+  #define LCD_I2C_PIN_EN  2
+  #define LCD_I2C_PIN_RW  1
+  #define LCD_I2C_PIN_RS  0
+  #define LCD_I2C_PIN_D4  4
+  #define LCD_I2C_PIN_D5  5
+  #define LCD_I2C_PIN_D6  6
+  #define LCD_I2C_PIN_D7  7
+
+  #include <Wire.h>
+  #include <LCD.h>
+  #include <LiquidCrystal_I2C.h>
+  #define LCD_CLASS LiquidCrystal_I2C
+  LCD_CLASS lcd(LCD_I2C_ADDRESS,LCD_I2C_PIN_EN,LCD_I2C_PIN_RW,LCD_I2C_PIN_RS,LCD_I2C_PIN_D4,LCD_I2C_PIN_D5,LCD_I2C_PIN_D6,LCD_I2C_PIN_D7);
+  
+#elif defined(LCD_I2C_TYPE_MCP23017)
+  //for the LED indicators (which maybe mapped to different things in lcd_implementation_update_indicators())
+  #define LED_A 0x04 //100
+  #define LED_B 0x02 //010
+  #define LED_C 0x01 //001
+
+  #define LCD_HAS_STATUS_INDICATORS
+
+  #include <Wire.h>
+  #include <LiquidTWI2.h>
+  #define LCD_CLASS LiquidTWI2
+  LCD_CLASS lcd(LCD_I2C_ADDRESS);
+  
+#elif defined(LCD_I2C_TYPE_MCP23008)
+  #include <Wire.h>
+  #include <LiquidTWI2.h>
+  #define LCD_CLASS LiquidTWI2
+  LCD_CLASS lcd(LCD_I2C_ADDRESS);  
+  
+#else
+  // Standard directly connected LCD implementations
+  #if LANGUAGE_CHOICE == 6
+    #include "LiquidCrystalRus.h"
+    #define LCD_CLASS LiquidCrystalRus
+  #else 
+    #include <LiquidCrystal.h>
+    #define LCD_CLASS LiquidCrystal
+  #endif  
+  LCD_CLASS lcd(LCD_PINS_RS, LCD_PINS_ENABLE, LCD_PINS_D4, LCD_PINS_D5,LCD_PINS_D6,LCD_PINS_D7);  //RS,Enable,D4,D5,D6,D7
 #endif
 
 /* Custom characters defined in the first 8 characters of the LCD */
     lcd.setBacklightPin(LCD_I2C_PIN_BL,POSITIVE);
     lcd.setBacklight(HIGH);
   #endif
+  
 #elif defined(LCD_I2C_TYPE_MCP23017)
   	lcd.setMCPType(LTI_TYPE_MCP23017);
     lcd.begin(LCD_WIDTH, LCD_HEIGHT);
     lcd.setBacklight(0); //set all the LEDs off to begin with
+    
 #elif defined(LCD_I2C_TYPE_MCP23008)
   	lcd.setMCPType(LTI_TYPE_MCP23008);
     lcd.begin(LCD_WIDTH, LCD_HEIGHT);
+    
 #else
     lcd.begin(LCD_WIDTH, LCD_HEIGHT);
 #endif
     //Status message line on the last line
     lcd.setCursor(0, LCD_HEIGHT - 1);
     lcd.print(lcd_status_message);
-#ifdef LCD_HAS_STATUS_INDICATORS
-    lcd_implementation_update_indicators();
-#endif    
 }
 static void lcd_implementation_drawmenu_generic(uint8_t row, const char* pstr, char pre_char, char post_char)
 {
 
 static void lcd_implementation_quick_feedback()
 {
-#ifdef LCD_HAS_I2C_BUZZ
+#ifdef LCD_USE_I2C_BUZZER
     lcd.buzz(300,4000);
 #elif defined(BEEPER) && BEEPER > -1
     SET_OUTPUT(BEEPER);
 }
 #endif
 
-#ifdef LCD_HAS_EXTRA_BUTTONS
-static uint8_t lcd_read_extra_buttons()
+#ifdef LCD_HAS_SLOW_BUTTONS
+static uint8_t lcd_implementation_read_slow_buttons()
 {
   #ifdef LCD_I2C_TYPE_MCP23017
-    // the I2C button bit positions are shifted by three bits from the native LiquidTWI2 position
-    // this is potentially too slow to call inside interrupt context
+    // Reading these buttons this is likely to be too slow to call inside interrupt context
+    // so they are called during normal lcd_update
     return lcd.readButtons() << B_I2C_BTN_OFFSET; 
   #endif
 }