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Simple EEPROM Driver for AVR Processors with RAM Stack
Adapted from the work of Sean Ellis

Download the test program with driver:  i2cm030710F.asm

I had been putting off writing a driver for some 24LC64 and 24LC256 EEPROMS I was thinking about using, when I came across a temperature logger application written by Sean Ellis. The Temperature logger was posted on on www.avrfreaks.net on January 10, 2002, project ID 49.  The original application was written for the ATtiny15,  which has a small hardware stack, so when extracting the I2C code, I massaged it a little bit to make it more compact when running on processors equipped with a RAM stack while making it a little easier to customize for new applications. The block write was omitted. If you need higher writing throughput, have a look at the original code on www.avrfreaks.net.

The resulting code was run in a small test program in an AT90S2313.

Customiztion and use

Pull-up resistors are required on SDA and SCL lines. See the I2C spec. for details.

The subroutine, I2CInit, needs to be called during initialization, preferable after the I/O ports are initialized but before calling any I2C read or write routines. I2CInit will set up the I2C I/O pins and initialize the bus.

The EEPROM code needs to be customized to deal with the I/O pins being used and the  processor clock speed in each particular application. All constants and registers that need to be modified are found  in the I2C Memory Driver section. Check and if necessary, change the I/O assignments to I2CPORT, I2CDDR,  I2CPIN, bSDA, and bSCL in the I2C Memory Driver sect

Delays to accommodate various bus speed and processor clock rates are controlled by the constant I2CDelayConstant.

The device address constant (ADDR24LC64 in this case) needs to match that of the EEPROM being used. The 24LC64, 24LC128. and 24LC256 use address A0 when their address pins are tied low.

There are two main subroutines of interest.

WriteI2Mem writes the byte contained in register "I2WData" into the EEPROM location pointed to by ZH,ZL.

ReadI2Mem reads the byte at the EEPROM location pointed to by ZH,ZL and returns the byte in register "temp".

There are no provision within the subroutines to check for invalid addresses.


Rights

The code, as far as I  know, is in the public domain.

Please see the liability disclaimer on the HOME page.
Contents ©2003 Richard Cappels All Rights Reserved . http://projects.cappels.org/
Minor spelling correction June, 2011.

Unabashed plug: Consulting is available.