24AA65/24LC65/24C65
3.3
Stop Data Transfer (C)
2.0
FUNCTIONAL DESCRIPTION
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.
The 24XX65 supports a bidirectional two-wire bus and
data transmission protocol. A device that sends data
onto the bus is defined as transmitter, and a device
receiving data as receiver. The bus must be controlled
by a master device which generates the serial clock
(SCL), controls the bus access and generates the Start
and Stop conditions, while the 24XX65 works as slave.
Both master and slave can operate as transmitter or
receiver, but the master device determines which mode
is activated.
3.4
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.
The data on the line must be changed during the low
period of the clock signal. There is one clock pulse per
bit of data.
3.0
BUS CHARACTERISTICS
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.
The following bus protocol has been defined:
• Data transfer may be initiated only when the bus
is not busy.
• 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.
3.5
Acknowledge
Each receiving device, when addressed, is obliged 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.
Accordingly, the following bus conditions have been
defined (Figure 3-1).
Note:
The 24XX65 does not generate any
Acknowledge bits if an internal program-
ming cycle is in progress.
3.1
Bus not Busy (A)
Both data and clock lines remain high.
A device that acknowledges must 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. During
reads, 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 (24XX65) must leave the data line high to enable
the master to generate the Stop condition.
3.2
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.
FIGURE 3-1:
DATA TRANSFER SEQUENCE ON THE SERIAL BUS
(A)
(B)
(D)
(D)
(C)
(A)
SCL
SDA
Start
Condition
Stop
Condition
Address or
Acknowledge
Valid
Data
Allowed
To Change
2003 Microchip Technology Inc.
DS21073J-page 5
MICROCHIP [ MICROCHIP ]
