PT7C4372A Datasheet, PDF (23/30 Pages) Pericom Semiconductor Corporation – Real-time Clock Module

PT7C4372A/4372C
Real-time Clock Module (I²C Bus)
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Data Transfers and Acknowledge Responses during I²C-BUS Communication
1) Data transfers
Data transfers are performed in 8-bit (1 byte) units once the START condition has occurred. There is no limit on the amount
(bytes) of data that are transferred between the START condition and STOP condition. (However, the transfer time must be no
longer than 0.5 seconds and access to the Address Dh (Reserved) register is prohibited.)
The address auto increment function operates during both write and read operations. After address Fh, increment goes to address
0h. Updating of data on the transmitter (transmitting side)'s SDA line is performed while the SCL line is at low level. The receiver
(receiving side) captures data while the SCL line is at high level.
*Note with caution that if the SDA data is changed while the SCL line is at high level, it will be treated as a START, RESTART,
or STOP condition.
2) Data acknowledge response (ACK signal)
When transferring data, the receiver generates a confirmation response (ACK signal, low active) each time an 8-bit data segment
is received. If there is no ACK signal from the receiver, it indicates that normal communication has not been established. (This
does not include instances where the master device intentionally does not generate an ACK signal.)
Immediately after the falling edge of the clock pulse corresponding to the 8th bit of data on the SCL line, the transmitter releases
the SDA line and the receiver sets the SDA line to low (= acknowledge) level.
SCL from Master
1
2
8
9
SDA from transmitter
(sending side)
SDA from receiver
(receiving side)
Release SDA
Low active
ACK signal
After transmitting the ACK signal, if the Master remains the receiver for transfer of the next byte, the SDA is released at the
falling edge of the clock corresponding to the 9th bit of data on the SCL line. Data transfer resumes when the Master becomes the
transmitter.
When the Master is the receiver, if the Master does not send an ACK signal in response to the last byte sent from the slave that
indicates to the transmitter that data transfer has ended. At that point, the transmitter continues to release the SDA and awaits a
STOP condition from the Master.
12-07-0001
PT0150-8 07/04/12
23