Bruno,

There is one subroutine below you are looking for

;Receiving Byte From AT24C256 via I2C bus
FRAT24: SETB SDA ;Leave data bus
MOV B,#8 ;Bit counter
FRAT1: SETB SCL ;Strobe beginning
MOV C,SDA ;Put current bit
RLC A ;into accumalator
CLR SCL ;End of strobe
DJNZ B,FRAT1 ;All bites?
CLR SDA ;Put ACK bit
SETB SCL ;Last
NOP ;strobe on
CLR SCL ;clock bus
RET

Hope it helps you. Don't turn over the Earth(:-).

Regards,
George