M4T28-BR12SH ST Microelectronics, M4T28-BR12SH Datasheet - Page 11

• Manufacturer Part Number: M4T28-BR12SH
• Description: TIMEKEEPER SNAPHAT Battery & Crystal
• Manufacturer: ST Microelectronics

Data Valid. 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 may be changed
during the Low period of the clock signal. There is
one clock pulse per bit of data.
Each data transfer is initiated with a start condition
and terminated with a stop condition. The number
of data bytes transferred between the start and
stop conditions is not limited. The information is
transmitted byte-wide and each receiver acknowl-
edges with a ninth bit.
By definition a device that gives out a message is
called “transmitter,” the receiving device that gets
the message is called “receiver.” The device that
controls the message is called “master.” The de-
vices that are controlled by the master are called
“slaves.”
Figure 9. Serial Bus Data Transfer Sequence
Figure 10. Acknowledgement Sequence
SCL FROM
MASTER
DATA OUTPUT
BY TRANSMITTER
DATA OUTPUT
BY RECEIVER
CLOCK
DATA
CONDITION
START
START
MSB
1
DATA VALID
DATA LINE
STABLE
DATA ALLOWED
CHANGE OF
2
Acknowledge. Each byte of eight bits is followed
by one Acknowledge Bit. This Acknowledge Bit is
a low level put on the bus by the receiver whereas
the master generates an extra acknowledge relat-
ed clock pulse. A slave receiver which is ad-
dressed is obliged to generate an acknowledge
after the reception of each byte that has been
clocked out of the slave transmitter.
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 a stable Low dur-
ing the High period of the acknowledge related
clock pulse. Of course, setup and hold times must
be taken into account. A master receiver must sig-
nal an end of data to the slave transmitter by not
generating an acknowledge on the last byte that
has been clocked out of the slave. In this case the
transmitter must leave the data line High to enable
the master to generate the STOP condition.
LSB
8
M41ST85Y, M41ST85W
ACKNOWLEDGEMENT
CLOCK PULSE FOR
CONDITION
STOP
9
AI00601
AI00587
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