Add update() method.

README.md

@@ -1,4 +1,4 @@
-# Arduino EEPROM Library
++++++# Arduino EEPROM Library
 http://github.com/JChristensen/JC_EEPROM  
 README file  
 
@@ -25,6 +25,8 @@ The **JC_EEPROM Library** has been tested with:
 - Microchip 24LC256 (256k bit)
 - Microchip 24FC1026 (1M bit, thanks to Gabriele B on the Arduino forum)
 - ST Micro M24M02 (2M bit)
+- Atmel AT24C256C (thanks to searobin)
+- Microchip 24C16B, 24C32 (thanks to Diogko)
 
 The **JC_EEPROM Library** will **NOT** work with Microchip 24xx1025 as its control byte does not conform to the following assumptions.
 
@@ -108,7 +110,7 @@ if ( i2cStat != 0 ) {
 	//there was a problem
 }
 ```
-### write(unsigned long addr, byte *values, unsigned int nBytes)
+### write(unsigned long addr, byte* values, unsigned int nBytes)
 ##### Description
 Write one or more bytes to external EEPROM.
 ##### Syntax
@@ -149,11 +151,11 @@ Same as multiple-byte write() above.
 //write the value 16 to EEPROM location 314.
 byte i2cStat = myEEPROM.write(314, 16);
 ```
-### read(unsigned long addr, byte *values, unsigned int nBytes)
+### read(unsigned long addr, byte* values, unsigned int nBytes)
 ##### Description
 Reads one or more bytes from external EEPROM into an array supplied by the caller.
 ##### Syntax
-`myEEPROM.read(unsigned long addr, byte *values, byte nBytes);`
+`myEEPROM.read(unsigned long addr, byte* values, byte nBytes);`
 ##### Parameters
 **addr** *(unsigned long)*: The beginning EEPROM location to read from.  
 **values** _(byte*)_: Pointer to an array to receive the data.  
@@ -203,3 +205,19 @@ else {
 	//data read ok
 }
 ```
+
+### update(unsigned long addr, byte value)
+##### Description
+Updates a single byte in external EEPROM. Like `write(addr, value)` except first reads the location from EEPROM and only writes `value` if it differs from the current value stored at the given location, to reduce wear on the EEPROM.
+##### Syntax
+`myEEPROM.update(unsigned long addr, byte value);`
+##### Parameters
+**addr** *(unsigned long)*: The EEPROM location to update.  
+**values** _(byte)_: The value to write.  
+##### Returns
+Same as multiple-byte write() above.
+##### Example
+```c++
+// update the value in EEPROM location 314 to 16.
+byte i2cStat = myEEPROM.update(314, 16);
+```

src/JC_EEPROM.h

@@ -79,18 +79,22 @@ class JC_EEPROM
         };
 
         // I2C clock frequencies
-        enum twiClockFreq_t { twiClock100kHz = 100000, twiClock400kHz = 400000 };
+        enum twiClockFreq_t
+            { twiClock100kHz = 100000, twiClock400kHz = 400000 };
 
         // EEPROM addressing error, returned by write() or read() if
         // upper address bound is exceeded
         static const uint8_t EEPROM_ADDR_ERR {9};
 
-        JC_EEPROM(eeprom_size_t deviceCapacity, byte nDevice, unsigned int pageSize, byte eepromAddr = 0x50);
+        JC_EEPROM(eeprom_size_t deviceCapacity, byte nDevice,
+            unsigned int pageSize, byte eepromAddr = 0x50);
         byte begin(twiClockFreq_t twiFreq = twiClock100kHz);
         byte write(unsigned long addr, byte* values, unsigned int nBytes);
         byte write(unsigned long addr, byte value);
         byte read(unsigned long addr, byte* values, unsigned int nBytes);
         int read(unsigned long addr);
+        byte update(unsigned long addr, byte value)
+            {return (read(addr) == value) ? 0 : write(addr, &value, 1); }
 
     private:
         uint8_t _eepromAddr;            // eeprom i2c address