S524A40X11/40X21/40X41/60X81/60X51 SERIAL EEPROM

DATA SHEET

1-6

I

Here are several rules for I

— A new data transfer can be initiated only when the bus is currently not busy.

— MSB is always transferred first in transmitting data.

— During a data transfer, the data line (SDA) must remain stable whenever the clock line (SCL) is High.

The I

•

Bus not busy: The SDA and the SCL lines remain High level when the bus is not active.

•

Start condition: Start condition is initiated by a High-to-Low transition of the SDA line while SCL remains High

level. All bus commands must be preceded by a start condition.

•

Stop condition: A stop condition is initiated by a Low-to-High transition of the SDA line while SCL remains

High level. All bus operations must be completed by a stop condition (see Figure 1-7).

SCL

SDA

Start

Condition

Data or

ACK Valid

Data

Change

Stop

Condition

Figure 1-7. Data Transmission Sequence

•

Data valid: Following a start condition, the data becomes valid if the data line remains stable for the duration

of the High period of SCL. New data must be put onto the bus while SCL is Low. Bus timing is one clock

pulse per data bit. The number of data bytes to be transferred is determined by the master device. The total

number of bytes that can be transferred in one operation is theoretically unlimited.

•

ACK (Acknowledge): An ACK signal indicates that a data transfer is completed successfully. The transmitter

(the master or the slave) releases the bus after transmitting eight bits. During the 9th clock, which the master

generates, the receiver pulls the SDA line low to acknowledge that it successfully received the eight bits of

data (see Figure 1-8). But the slave does not send an ACK if an internal write cycle is still in progress.

In data read operations, the slave releases the SDA line after transmitting 8 bits of data and then monitors

the line for an ACK signal during the 9th clock period. If an ACK is detected, the slave will continue to

transmit data. If an ACK is not detected, the slave terminates data transmission and waits for a stop condition

to be issued by the master before returning to its stand-by mode.