M24SR64-Y Datasheet, PDF (57/90 Pages) STMicroelectronics – Support of NDEF data structure

M24SR64-Y
7
I²C device operation
I2C device operation
7.1
Note:
The M24SR64-Y device supports the I²C protocol. The device that controls the data transfer
is known as the bus master, and the other one as the slave device. A data transfer can only
be initiated by the bus master, which also provides the serial clock for synchronization. The
M24SR64-Y device is a slave in all communications.
I²C communication protocol
The I²C communication is built on a system of command and reply exchange. The I²C host
starts the communication by sending a request. Once a valid request is received by the
M24SR64-Y device, it carries out an internal operation and creates its answer.
As defined in this document, and except for the GetI2C session and Kill RF session
commands, the definition of a valid request is a command with a right CRC value.
Figure 12 shows an exchange of a command and a response between the I²C host and the
M24SR64-Y. Once the I²C session is open, the I²C host can send a command. The
command is composed of:
• a Device Select field with the R/W bit set to 0.
• the command field.
The M24SR64-Y acknowledges on the reception of each byte.
Once the M24SR64-Y is ready to send the answer, the I²C host shall:
• send a Device Select field with the R/W bit set to 1.
• release the SDA line and send an SCL clock.
The I²C host shall acknowledge on the reception of each byte.
Figure 12. Command and response exchange
,&EXV
5: 
6 'HYLFH6HOHFW
&RPPDQG 3
5: 
6 'HYLFH6HOHFW
5HVSRQVH 3
069
Legend:
S is the I²C Start bit sequence
P is the I²C Stop bit sequence
R/W is the 8^th bit of Device Select.
A restart during a command and response exchange is not supported by the M24SR64-Y.
After a command, the I²C host can execute a Polling sequence to determine when the
response is available.
Polling sequence: Loop on < START (S) + DeviceSelect with RW=0 + read NACK/ACK
+ STOP (P) >
The response is available as soon as the M24SR64-Y sends an ACK ( host read will a
'0').
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