Spency's digital-diy 18F PIC micro Tutorial

18F External EEPROM Example

External EEPROMS are great for storing data, and to interface with them is not all that hard. Most use the I2C protocol. In this example the 24LC256 is used. I2C communication is great as it can allow serial data communication between many devices on a single 2 wire bus. These two lines are referred too as SDA and SCL. Basically SDA is the serial data and SCL maintains the clock/frequency in which data is transferred.

Like most peripherals, I've made my own Swordfish Library for the 24LC series EEPROM's. Pins 1, 2, 3 set the address of the EEPROM. As you can see in the diagram below, the highest 24LC256 has one connection to earth (Pin 3), and two connections to 5V (Pins 1 & 2).. this defines it as %011 (don't forget that binary starts from the right!) on the I2C Bus.

Pin 4 on 24LC256 = Vss (Earth)
Pin 8 on 24LC256 = Vdd (5V)
Note the PIC's power supply/oscillator are not shown

Click here to see this circuit in action!

Here is an example of how to use the Library with a single EEPROM (24LC256)

Device = 18F452
Clock = 20
// import libraries...
Include "ExtEEPROM.bas"
Include "usart.bas" 
Include "Convert.bas"
Dim 
    Variable As Byte,       // Variable used for data 
    Device_Address As Byte, // Register for I2C Address reference
    Memory_Address As Byte, // Register for EEPROM memory address
    Family As Byte          // Register for External EEPROM family setting
    
    USART.SetBaudrate(br19200) 
    
    Variable = 123          // Place the value "1" in the variable register
    Device_Address = %000   // Set the EEPROM I2C address
    Memory_Address = 10     // Set the EEPROM address location to 0
    Family = %1010          // Set the Family configeration as the binary number 1010
    // Write the value 123 to EEPROM 000 at memory location 10
    ExtEEPROM.Write(Variable, Memory_Address, Device_Address, Family)        
    // Read from EEPROM 000, memory location 10
    Variable = ExtEEPROM.Read(Memory_Address, Device_Address, Family)
    
    USART.Write(Convert.DecToStr(Variable))
    
    While True
    Wend

Video Tutorials:

Single External EEPROM use with Spency's Library
Explores the use of the External EEPROM Library
Covers the "Family" register use for compatibility with other EEPROM's
** Note - I mention that 10mS is required after an EEPROM write, this is now part of the Library and is not required **
Multiple (4) External EEPROM's and Spency's Library
Covers the use of addressing multiple EEPROM's on the I2C Bus with the Library

Download Spency's External EEPROM Library