Two-wire Serial EEPROM
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 (refer to Figure 4). Data changes during SCL high periods will indicate a
start or stop condition as defined below.
A high-to-low transition of SDA with SCL high is a start condition which must precede any other
command (refer to Figure 5).
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 (refer to Figure 5).
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 :
The ACE24C128/256 features a low-power standby mode which is enabled: (a) upon power-up and (b)
after the receipt of the stop bit and the completion of any internal operations.
Memory Reset :
After an interruption in protocol power loss or system reset, any two-wire part can be protocol reset by following
1. Clock up to 9 cycles.
2. Look for SDA high in each cycle while SCL is high and then.
3. Create a start condition as SDA is high.
Figure 2.SCL: Serial Clock, SDA: Serial Data I/O
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