24AA024/24LC024/24AA025/24LC025
The data on the line must be changed during the low
period of the clock signal. There is one bit of data per
clock pulse.
4.0
BUS CHARACTERISTICS
The following bus protocol has been defined:
• Data transfer may be initiated only when the bus
is not busy.
Each data transfer is initiated with a Start condition and
terminated with a Stop condition. The number of the
data bytes transferred between the Start and Stop
conditions is determined by the master device and is,
theoretically, unlimited (though only the last sixteen will
be stored when performing a write operation). When an
overwrite does occur, it will replace data in a first-in
first-out fashion.
• During data transfer, the data line must remain
stable whenever the clock line is high. Changes in
the data line while the clock line is high will be
interpreted as a Start or Stop condition.
Accordingly, the following bus conditions have been
defined (Figure 4-1).
4.5
Acknowledge
4.1
Bus Not Busy (A)
Each receiving device, when addressed, is required to
generate an acknowledge after the reception of each
byte. The master device must generate an extra clock
pulse, which is associated with this Acknowledge bit.
Both data and clock lines remain high.
4.2
Start Data Transfer (B)
A high-to-low transition of the SDA line while the clock
(SCL) is high determines a Start condition. All
commands must be preceded by a Start condition.
Note:
The 24AA024/24LC024/24AA025/24LC025
does not generate any Acknowledge bits if
an internal programming cycle is in prog-
ress.
4.3
Stop Data Transfer (C)
The device that acknowledges has to pull down the SDA
line during the acknowledge clock pulse in such a way
that the SDA line is stable low during the high period of
the acknowledge-related clock pulse. Of course, setup
and hold times must be taken into account. A master
must signal an end of data to the slave by not generating
an Acknowledge bit on the last byte that has been
clocked out of the slave. In this case, the slave must
leave the data line high to enable the master to generate
the Stop condition (Figure 4-2).
A low-to-high transition of the SDA line while the clock
(SCL) is high determines a Stop condition. All
operations must be ended with a Stop condition.
4.4
Data Valid (D)
The state of the data line represents valid data when,
after a Start condition, the data line is stable for the
duration of the high period of the clock signal.
FIGURE 4-1:
DATA TRANSFER SEQUENCE ON THE SERIAL BUS CHARACTERISTICS
(A)
(B)
(C)
(D)
(C) (A)
SCL
SDA
Start
Condition
Stop
Condition
Address or
Acknowledge
Valid
Data
Allowed
to Change
FIGURE 4-2:
ACKNOWLEDGE TIMING
Acknowledge
Bit
1
2
3
4
5
6
7
8
9
1
2
3
SCL
SDA
Data from transmitter
Data from transmitter
Transmitter must release the SDA line at this point allowing
the Receiver to pull the SDA line low to acknowledge the
previous eight bits of data.
Receiver must release the SDA line at this
point so the Transmitter can continue
sending data.
DS21210N-page 6
© 2009 Microchip Technology Inc.
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