Why external EEPROM memory?
Sometimes small internal EEPROM memory in ST7 devices is not enough to application requirements. By connecting external EEPROM chips we can expand this small non-volatile memory space. Most popular EEPROMs are  24Cxx I2C bus memories.

We are use software I2C master routines from page : Software I2C master implementation

Pinout of M24C64 from STMicroelectronics (and other M24Cxx memories) is shown on below picture:

Pins E0..E2 are chip enable inputs. In dependency of this pins state memory device slave address can be different. Look at below table:

It can be up to eight different address of M24C64 memory, so we can connect up to eight of M24C64 memory devices to one I2C bus. Device select address is shown on below picture :

Write single byte to EEPROM memory
Write single byte to specified address in EEPROM memory is realized by a M24C64_WriteByte routine. Before call to m24DstAddr variable write destination address (memory cell address in M24C64 device) and to A register write byte to write in EEPROM memory.
Byte write sequence is shown on below picture :

Source code of M24C64_WriteByte routine is shown below :

Source code of M24C64_WriteByte routine

;------------------------------------------------------------------------- ; Parameters ; m24DstAddr : destination address ; A : data to write ;------------------------------------------------------------------------- .M24C64_WriteByte   PUSH A                   ; store data on stack   CALL I2C_Start           ; START   LD   A, #M24WRITEADDR    ;   CALL I2C_Write           ; address of M24C64   LD   A, {m24DstAddr + 0} ;   CALL I2C_Write           ; MSB of memory address   LD   A, {m24DstAddr + 1} ;   CALL I2C_Write           ; LSB of memory address   POP  A                   ; restore data from stack   CALL I2C_Write           ; data write   CALL I2C_Stop            ; STOP   RET

Write buffer to EEPROM memory
When we want write many bytes from continuous memory space to EEPROM memory write byte-by-byte is very ineffective. M24C64 memory device can write up to 32 bytes in one programming cycle. Page write sequence is shown on below picture :

Source code of M24C64_WriteBuffer routine is shown below:

Read single byte from EEPROM memory
Read single byte from M24C64 EEPROM memory is realized by a M24C64_ReadByte routine. Before call this routine place in m24SrcAddr address of read byte in memory. Single byte read sequence is shown on below picture:

Source code of M24C64_ReadByte routine is shown below:

Read buffer from EEPROM memory
Similar to write more than one byte, there are possibility to read more than one bytes from EEPROM memory. Continuous read sequence is shown on below picture :

Source code of M24C64_ReadBuffer routine is shown below:

Download
  M24C64.asm