RX
-
8025
SA
/
NB
Page - 24 ETM10E-04
8.8.3. Starting and stopping I
2
C bus communications
1) START condition, repeated START condition, and STOP condition
(1) START condition
• This condition regulates how communications on the I
2
C-BUS are started.
SDA level changes from high to low while SCL is at high level
(2) STOP condition
• This condition regulates how communications on the I
2
C-BUS are terminated.
SDA level changes from low to high while SCL is at high level
(3) 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.
Some important matters when RX8025 is controlled in I2C.
When a stop condition occurred during communication, SDA of RX8025 is freed to Hi-Z.
As a result, as for all the reading data after STOP, "1" is received.
This can cause data error in a system.
Data every 4 bits are stored to RX-8 025 in writing.
When writing, Data every 4 bits are stored to RX-8025.
Therefore, it is written in at the RTC inside to 4 bits (nybble) just before that when a stop condition
occurs during write-access.
When update of the clock counters occurs during serial communication, the error that read/write data
become false setting occurs.
Therefore, update of a clock counter of RX8025 is stopped temporarily to prevent this error when
RX8025 receives a start condition.
A update of clock counter is revised , afterwards when RX8025 receives a stop condition.
And clock of RX8025 is started again immediately.
However, for example, a RX8025 time continues stopping when STOP is not transmitted by power
supply troubles of a host.
To evade this problem, RX8025 re-start counters of clock, when a stop-condition is not received even if
2Hz (0.5 seconds) pulse two times occurs at inside counter of RX-8025.
And I2C interface is reset.
As a result, SDA becomes Hi-Z, and all the reading data become "1".
Please consider the following communication conditions to operate this compensation function
precisely.
In I2C communication, please complete stop condition from the first start condition within 0.5 second.
Re-START condition are included in 0.5second.
When restart occurs, RX-8 025 stops the time once more, and it is it for 2Hz pulse twice waiting.
Therefore, when restart continued occurring in a short time, clock pause is not released.
As a result, the time will delay very much.
And waiting more than 62 s(Min.) is necessary from the transmission of a stop condition to the
transmission of a next start condition.
Update of the clock which occurred during I2C communication is corrected in 62us(Min.).
Therefore RX8025 time delay when this waiting is short.
This time compensation function of RX8025 is possible only one second.
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