This application note was written by Victoria Welch from code supplied by Brent Nelson.
Download the zipped file or copy / paste from below.
The zip file contains the following code and a schematic which may be useful to assemble a test circuit for this program.
'**********************************************************************
' Application Note: 16 Bit Addressing on the I2C Bus.
' (8 bit data transfers one byte at a time)
'-----------------------------------------------------
'
' Program-ID.: I2C_EEPROM.bas.
' Date...... : 04 / 04 / 2002
' Description: Example program for I2c EEprom write and read routines
'
' Author : Victoria Welch (vikki@oz.net).
' This program finally helped me get my 24LC64 EEPROM working.
' Many thanks Brent! I Converted the original program into an
' application note in the hope it helps others new to these devices.
'
' Brent Nelson (spock50@gte.net).
' Brent provided the orginal form of this program to the BASCOM list.
'
' Remarks:
' Setup for the AT90S2313 using portb.0 for SDA and Portb.1 for SCL.
'
' Uses onboard serial port.
'
' This program provides an example for writing to and reading from
' an I2C EEPROM device wired for device 0 (AO,A1 and A2 all pulled
' to Gnd).
'
' This has been tested with a Microchip 24LC65.
'
'**********************************************************************
$regfile = "2313def.dat" ' Change for your AVR.
$crystal = 4000000 ' 4 MHz Crystal.
$baud = 9600 ' Output at 9600 baud.
'**********************************************************************
'** Set up Data Direction Registers and ports - Do this before defining I2C pins!
'** Read up on this in the data sheet, understanding is important!
'**********************************************************************
' Port B
Portb = &B0000_0000 ' Set All Port Pins Low
Ddrb = &B1111_1100 ' Set Unused Pins As Outputs. Set I2C pins as inputs (tri-state- floating)
' Port D
Portd = &B0000_0000 ' All low - with push-pull output
Ddrd = &B1111_1111 ' with internal pullups.
'**********************************************************************
'** Define and initialize I2C pins **
'**********************************************************************
Config Sda = Portb.0 ' I2C Data.
Config Scl = Portb.1 ' I2C Clock.
'**********************************************************************
'** Declate subroutines **
'**********************************************************************
'
' This subroutine writes data to the I2C EEPROM.
'
Declare Sub I2c_ram_write(address_desired As Word , Content As Byte)
'
' This subroutine reads data from the I2C EEPROM.
'
Declare Sub I2c_ram_read(address_desired As Word)
'**********************************************************************
'** Define working variables and constants **
'**********************************************************************
Dim I2c_eeprom_address_desired As Word ' I2C EEPROM address counter (provides for 65536 locations).
Dim I2c_eeprom_address_high_byte As Byte ' High byte of EEPROM address.
Dim I2c_eeprom_address_low_byte As Byte ' Low byte of EEPROM address.
Dim Data_work_var As Byte ' Working variables.
Dim Counter As Byte
'
' Change the 3 "AD" bits to reflect the I2C address of the device
' (corresponding to A0,A1 and A2)..
' FAM AD M
Const Eeprom_chip_write_command = &B10100000 ' Family "A", Device/unit 1, write.
Const Eeprom_chip_read_command = &B10100001 ' Family "A", Device/unit 1, Read.
'**********************************************************************
'** Actual work starts here. **
'**********************************************************************
Main:
Print "I2C EEPROM Test Program." ' Just a header for separation.
'
' First we write data to the EEPROM: 150 to 51
'
Counter = 100 ' Initialize loop counter.
I2c_eeprom_address_desired = 0 ' We start writing at EEPROM address zero.
Do
Data_work_var = Counter + 50 ' Generate test data (=0<256).
Call I2c_ram_write(i2c_eeprom_address_desired , Data_work_var) ' Write it to the EEPROM.
Incr I2c_eeprom_address_desired ' Increment EEPROM address location desired.
Decr Counter ' Decrement the loop counter.
Loop Until Counter = 0
Print "All locations written to." ' Tell what is going on.
'
' Now we read that data back. If returned data is all 255s check your circuit.
'
Counter = 100 ' initialize loop counter.
I2c_eeprom_address_desired = 0 ' We start reading at EEPROM address zero.
Do
Call I2c_ram_read(i2c_eeprom_address_desired) ' Call sub to read from device.
Print "Location: " ; Counter ; "=" ; Data_work_var ' Display data read from device.
Incr I2c_eeprom_address_desired ' Increment address counter.
Decr Counter ' Decrement loop counter.
Waitms 250 ' A little delay to watch the numbers go by.
Loop Until Counter = 0
Print "All locations read back, program ends." ' Tell what is going on.
End ' Program ends.
'**********************************************************************
'** Define Subroutines **
'**********************************************************************
Sub I2c_ram_write(address_desired As Word , Content As Byte) ' Writes data to the I2C EEPROM.
I2c_eeprom_address_low_byte = Low(address_desired) ' Extract low byte of address to be written.
I2c_eeprom_address_high_byte = High(address_desired) ' Extract high byte of addesss to be written.
I2cstart ' Send I2C Start.
I2cwbyte Eeprom_chip_write_command ' Select MicroChip EEPROM device type, address and write bit.
I2cwbyte I2c_eeprom_address_high_byte ' Send high address to write to.
I2cwbyte I2c_eeprom_address_low_byte ' Send low address to write to.
I2cwbyte Content ' Send the data to be written.
If Err = 0 Then ' check status of operation.
Print "Write is good: Location: " ; Address_desired ' Report success.
Else ' or
Print "Write failed: Location: " ; Address_desired ' Report failure.
End If
I2cstop ' All we want to do is done.
Waitms 10 ' Wait for write to finish up.
End Sub
Sub I2c_ram_read(address_desired As Word) ' Reads data from the I2C EEPROM.
I2c_eeprom_address_low_byte = Low(address_desired) ' Extract low byte of address to be read.
I2c_eeprom_address_high_byte = High(address_desired) ' Extract high byte of address to be read.
I2cstart ' Send I2C Start..
I2cwbyte Eeprom_chip_write_command ' Select MicroChip EEPROM device type, address and write bit
I2cwbyte I2c_eeprom_address_high_byte ' Send high byte of address to read from.
I2cwbyte I2c_eeprom_address_low_byte ' Send low byte of address to read from.
I2cstart ' Issue another start sequence.
I2cwbyte Eeprom_chip_read_command ' Select MicroChip EEPROM device type, address and read bit
I2crbyte Data_work_var , Nack ' Read data from desired location in chip.
If Err = 0 Then ' Check status of operation.
Print "Read is good: " ; ' Report success.
Else ' or
Print "Read failed: " ; ' Reeort failure.0
End If
I2cstop ' All we want to do is done.
End Sub