// Written by Nick Gammon
// 10th March 2011

#include <SPI.h>

#define CHIP_SELECT 10   // for EEPROM
#define BUFFER_ENABLE 9  // for SN54AHC125 buffer

// AT25DF041A EEPROM commands

// reading
#define ReadArray             0x0B
#define ReadArrayLowFrequency 0x03

// programming
#define BlockErase4Kb       0x20
#define BlockErase32Kb      0x52
#define BlockErase64Kb      0xD8
#define ChipErase           0x60
#define ByteProgram         0x02
#define SequentialProgram   0xAD

// protection
#define WriteEnable           0x06
#define WriteDisable          0x04
#define ProtectSector         0x36
#define UnProtectSector       0x39
#define ReadSectorProtection  0x3C

// status
#define ReadStatus 0x05
#define WriteStatus 0x01

// miscellaneous
#define ReadManufacturer     0x9F
#define DeepPowerDown        0xB9
#define ResumeFromPowerDown  0xAB

// wait until chip not busy
void notBusy ()
{
  digitalWrite (CHIP_SELECT, LOW);
  SPI.transfer (ReadStatus);       
  // wait until busy bit cleared
  while (SPI.transfer (0) & 1) 
     {} 
  digitalWrite (CHIP_SELECT, HIGH);  
}  // end notBusy

// enable writing
void writeEnable ()
{
 notBusy ();
 
 digitalWrite (CHIP_SELECT, LOW);
 SPI.transfer (WriteEnable);       
 digitalWrite (CHIP_SELECT, HIGH);  
}  // end of writeEnable

// read device status
byte readStatus (void)
{
 digitalWrite (CHIP_SELECT, LOW);
 SPI.transfer (ReadStatus);       
 byte status = SPI.transfer (status);       
 digitalWrite (CHIP_SELECT, HIGH);  
  
 return status;
}  // end of readStatus

// write status register
void writeStatus (const byte status)
{
   writeEnable ();
   notBusy ();  // wait until ready
   
   digitalWrite (CHIP_SELECT, LOW);
   SPI.transfer (WriteStatus);       
   SPI.transfer (status);       
   digitalWrite (CHIP_SELECT, HIGH);  
}  // end of writeStatus

// send a command to the EEPROM followed by a 3-byte address
void sendCommandAndAddress (const byte command, const unsigned long addr)
{
  SPI.transfer (command);       
  SPI.transfer ((addr >> 16) & 0xFF);       
  SPI.transfer ((addr >> 8) & 0xFF);       
  SPI.transfer (addr & 0xFF);       
}  // end of sendCommandAndAddress

// write len (max 256) bytes to device

// Note that if writing multiple bytes the address plus
//  length must not cross a 256-byte boundary or it will "wrap"
void writeEEPROM (const unsigned long addr, byte * data, int len) 
{
  // now write to it
  writeEnable ();
  
  notBusy ();  // wait until ready
  digitalWrite (CHIP_SELECT, LOW);
  sendCommandAndAddress (ByteProgram, addr);
  for ( ; len ; --len)
    SPI.transfer (*data++);       
  digitalWrite (CHIP_SELECT, HIGH);  
  notBusy (); 
} // end of writeEEPROM

// write one byte to device
void writeEEPROM (unsigned long addr, byte data) 
{
  writeEEPROM (addr, &data, 1);
} // end of writeEEPROM

// read len bytes from device
void readEEPROM (const unsigned long addr, byte * data, unsigned int len) 
{
  notBusy ();  // wait until ready
  digitalWrite (CHIP_SELECT, LOW);
  sendCommandAndAddress (ReadArray, addr);

  SPI.transfer (0);  // clock in "don't care" byte
 
  for ( ; len ; --len)
   *data++ = SPI.transfer (0);       
  digitalWrite (CHIP_SELECT, HIGH);  
  
}  // end of readEEPROM

// erase a 4Kb block of bytes which contains addr
void eraseEEPROM (const unsigned long addr)
{
  writeEnable ();

  notBusy ();  // wait until ready
  digitalWrite (CHIP_SELECT, LOW);
  sendCommandAndAddress (BlockErase4Kb, addr);
  digitalWrite (CHIP_SELECT, HIGH);  
  notBusy ();  // wait until done
  
}  // end of eraseEEPROM

// show device info and status
void info ()
{
  
  notBusy (); // wait until ready
  
  digitalWrite (CHIP_SELECT, LOW);
  SPI.transfer (ReadManufacturer);       
  
  Serial.print ("Manufacturer: ");
  Serial.println (SPI.transfer (0), HEX);
  Serial.print ("Device ID Part 1: ");
  Serial.println (SPI.transfer (0), HEX);
  Serial.print ("Device ID Part 2: ");
  Serial.println (SPI.transfer (0), HEX);
  Serial.print ("Extended Information Length: ");
  Serial.println (SPI.transfer (0),HEX);

  digitalWrite (CHIP_SELECT, HIGH);
  
  Serial.print ("Status: ");
  Serial.println (readStatus (), HEX);

} // end of info

void setup ()
{
  
  Serial.begin (9600);
  SPI.begin ();
   
  // enable the SN54AHC125 output enable peons (more work?)
  pinMode (BUFFER_ENABLE, OUTPUT);  // buffer chip enable
  digitalWrite (BUFFER_ENABLE,LOW);  // enable

  // global unprotect
  writeStatus (0);
  
  info ();
    
  // test: write a string to address 0x1000

#define TESTADDRESS 0x1000

  eraseEEPROM (TESTADDRESS);
  
  byte hello [] = "Hello, World!";
  
  writeEEPROM (TESTADDRESS, hello, sizeof hello);
  
  // read back to confirm
  byte test [sizeof hello] = { 0 } ;
  readEEPROM (TESTADDRESS, test, sizeof test);

  Serial.println ((char *) test);  // display to confirm
  
}  // end of setup

void loop()
{
 
}  // end of loop

  SPI.begin ();

  // Slow down the master a bit
  SPI.setClockDivider(SPI_CLOCK_DIV8);