6.
Device Operation
Clock and Data Transitions: The SDA pin is normally pulled high with an external device. Data on the SDA pin may
change only during SCL low time periods (See Figure 6-1). Data changes during SCL high periods will indicate a start or
stop condition as defined below.
Figure 6-1. Data Validity
SDA
SCL
Data Stable
Data Stable
Data
Change
Start Condition: A high-to-low transition of SDA with SCL high is a start condition that must precede any other command
(See Figure 6-2).
Figure 6-2. Start and Stop Definition
SDA
SCL
Start
Stop
Stop Condition: A low-to-high transition of SDA with SCL high is a stop condition. After a read sequence, the stop
command will place the EEPROM in a standby power mode (See Figure 6-2).
Acknowledge: All addresses and data words are serially transmitted to and from the EEPROM in 8-bit words. The
EEPROM sends a zero during the ninth clock cycle to acknowledge that it has received each word.
Standby Mode: AT24C128C features a low-power standby mode that is enabled upon power-up and after the receipt of
the stop bit and the completion of any internal operations.
Atmel AT24C128C [DATASHEET]
6
8734B–SEEPR–9/2012
ATMEL [ ATMEL ]
