ST24/25C16, ST24/25W16
Figure 6. I
2
C Bus Protocol
SCL
SDA
START
CONDITION
SDA
INPUT
SDA
CHANGE
STOP
CONDITION
SCL
1
2
3
7
8
9
SDA
MSB
ACK
START
CONDITION
SCL
1
2
3
7
8
9
SDA
MSB
ACK
STOP
CONDITION
AI00792
Stop Condition.
STOP is identified by a low to high
transition of the SDA line while the clock SCL is
stable in the high state. A STOP condition termi-
nates communication between the ST24/25x16
and the bus master. A STOP condition at the end
of a Read command forces the standby state. A
STOP condition at the end of a Write command
triggers the internal EEPROM write cycle.
Acknowledge Bit (ACK).
An acknowledge signal
is used to indicate a successful data transfer. The
bus transmitter, either master or slave, will release
the SDA bus after sending 8 bits of data. During the
9th clock pulse period the receiver pulls the SDA
bus low to acknowledge the receipt of the 8 bits of
data.
Data Input.
During data input the ST24/25x16
samples the SDA bus signal on the rising edge of
the clock SCL. Note that for correct device opera-
tion the SDA signal must be stable during the clock
low to high transition and the data must change
ONLY when the SCL line is low.
Memory Addressing.
To start communication be-
tween the bus master and the slave ST24/25x16,
the master must initiate a START condition. The 8
bits sent after a START condition are made up of a
device select of 4 bits that identifie the device type
(1010), 3 Block select bits and one bit for a READ
(RW = 1) or WRITE (RW = 0) operation.
There are three modes both for read and write.
They are summarised in Table 4 and described
hereafter. A communication between the master
and the slave is ended with a STOP condition.
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STMICROELECTRONICS [ STMICROELECTRONICS ]
