PT7C4372A Datasheet, PDF (22/30 Pages) Pericom Semiconductor Corporation – Real-time Clock Module

PT7C4372A/4372C
Real-time Clock Module (I²C Bus)
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Starting and Stopping I²C Bus Communications
Fig 5. Starting and stopping on I²C bus
1) START condition, repeated START condition, and STOP condition
a) START condition
SDA level changes from high to low while SCL is at high level
b) STOP condition
SDA level changes from low to high while SCL is at high level
c) Repeated START condition (RESTART condition)
In some cases, the START condition occurs between a previous START condition and the next STOP condition, in which
case the second START condition is distinguished as a RESTART condition. Since the required status is the same as for the
START condition, the SDA level changes from high to low while SCL is at high level.
2) Caution points
a) The master device always controls the START, RESTART, and STOP conditions for communications.
b) The master device does not impose any restrictions on the timing by which STOP conditions affect transmissions, so
communications can be forcibly stopped at any time while in progress. (However, this is only when this RTC module is in
receiver mode (data reception mode = SDA released).
c) When communicating with this RTC module, the series of operations from transmitting the START condition to
transmitting the STOP condition should occur within 0.5 seconds. (A RESTART condition may be sent between a START
condition and STOP condition, but even in such cases the series of operations from transmitting the START condition to
transmitting the STOP condition should still occur within 0.5 seconds.)
If this series of operations requires 0.5 to 1.0 seconds or longer, the I²C bus interface will be automatically cleared and set to
standby mode by this RTC module's bus timeout function. Note with caution that both write and read operations are invalid for
communications that occur during or after this auto clearing operation. (When the read operation is invalid, all data that is read has
a value of "1").
Restarting of communications begins with transfer of the START condition again.
d) When communicating with this RTC module, wait at least 1.3 µs between transferring a STOP condition (to stop
communications) and transferring the next START condition (to start the next round of communications). (If any carries occur in
the time data during this communication period, corrections are made during this period.)
Fig 6. Interval between start and st
12-07-0001
1.3
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PT0150-8 07/04/12