Update README.md

Cart_Reader/README.md

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-Double click on Cart_Reader.ino to open the program in the Arduino IDE.  
-And don't forget to copy the files from the sd folder to the root of your sd card.  
+This Arduino code is written by a beginner for beginners, therefore I tried to comment every line of code. To an experienced coder this probably will seem very wrong but it really helps if you're just starting out.   
+
+Source code files:   
+- Cart_Reader.ino is the main file that contains functions and variables being used by multiple submodules and also the main menu     
+- EEPROMAnything.h helps with reading and writing to the Atmega's internal eeprom   
+- FLASH.ino is for reading and writing 29F016, 29F032, 29F033, 29F1610 and 29L3211 flashroms   
+- GB.ino includes everything Game Boy and Game Boy Color   
+- GBA.ino includes everything Game Boy Advance   
+- N64.ino includes everything Nintendo 64   
+- NP.ino includes everything Nintendo Power/SF Memory Super Famicom Flashcarts   
+- SNES.ino includes everything Super Nintendo   
+
+Every submodule has it's own setup_XX() function that configures the needed pins and a submenu that lets you choose what you want to do. 
+The code directly addresses the pins via the DDR, PIN and PORT registers.   
+Please also refer to the [pinout Excel sheet] (https://github.com/sanni/cartreader/blob/master/pinout.xls).    
+```
+void setup_N64_Controller() {  
+  // Output a low signal  
+  PORTH &= ~(1 << 4);  
+  // Set Controller Data Pin(PH4) to Input  
+  DDRH &= ~(1 << 4);  
+}  
+```
+
+Would be the same as this in a more traditional Arduino sketch:  
+```
+int dataPin = 7;   
+
+void setup(){    
+  // Output a low signal   
+  digitalWrite(dataPin, LOW);   
+  // Set controller data pin to input  
+  pinMode(dataPin, INPUT);  
+}  
+```
+To preserve memory every string is saved into the flash of the Arduino, also called progmem. This is done by using the F() macro.   
+```
+println_Msg(F("Press Button."));  
+```
+Also all the menus are stored in progmem and are only recalled to sram when needed.  
+```
+// N64 controller menu items  
+const char N64ContMenuItem1[] PROGMEM = "Test Controller";  
+const char N64ContMenuItem2[] PROGMEM = "Read ControllerPak";  
+const char N64ContMenuItem3[] PROGMEM = "Write ControllerPak";  
+const char N64ContMenuItem4[] PROGMEM = "Reset";  
+const char* const menuOptionsN64Controller[] PROGMEM = {N64ContMenuItem1, N64ContMenuItem2, N64ContMenuItem3, N64ContMenuItem4};  
+```
+In an effort to keep the codebase as portable as possible instead of using the functions supplied by the OLED library directly to print out text helper functions like `println_Msg` are being used. So if you want to change to another display library you don't need to change all the code but only the helper functions. 
+```
+void print_Msg(long unsigned int message) {
+  if (enable_OLED)
+    display.print(message);
+  if (enable_Serial)
+    Serial.print(message);
+}
+```
+
+For development purposes you can route all the text output to the Arduino's Serial Monitor instead of to the OLED screen. In this case you control the cart reader by typing numbers into the serial monitor corresponding to the action you want to perform. If you are asked to press the button just send a random number.   
+```
+// If you don't have an OLED screen change  
+// enable_OLED to 0 and enable_Serial to 1   
+#define enable_OLED 0   
+#define enable_Serial 1   
+```
+
+To compile and upload the code please have a look at [this wiki article](https://github.com/sanni/cartreader/wiki/BASICS-How-to-flash-the-Arduino-Code-to-your-Cart-Reader).