
RS5C372A/B
34
1.2-6 Data transmission under special condition
The RS5C372A/B hold the clock tentatively for duration from start condition to stop condition to avoid invalid read
or write clock on carrying clock. When clock is carried during this period, which will be adjusted within approx.
61μs from stop condition. To prevent invalid read or write clock shall be made during one transmission operation
(from start condition to stop condition). When 0.5 to 1.0 second elapses after start condition any access to the
RS5C372A/B are automatically released to release tentative hold of the clock, set Fh to the address pointer, and
access from the CPU is forced to be terminated (the same action as made stop condition is received: automatic
resume function from the I
2
C bus interface). Therefore, one access must be completed within 0.5 seconds. The
automatic resume function prevents delay in clock even if the SCL is stopped from sudden failure of the system dur-
ing clock read operation.
Also a second start condition after the first condition and before the stop condition is regarded as the “repeated start
condition.” Therefore, when 0.5 to 1.0 seconds passed after the first start condition, access to the RS5C372A/B are
automatically released.
If access is tried after automatic resume function is activated, no acknowledge signal will be output for writing while
FFh will be output for reading.
Access to the Real-time Clock
1) No stop condition shall be generated until clock read/write is started and completed.
2) One cycle read/write operation shall be completed within 0.5 seconds.
The user shall always be able to access the real-time clock as long as these two conditions are met.
Bad example of reading from seconds to hours (invalid read)
(Start condition)
→
(Read of seconds)
→
(Read of minutes)
→
(Stop condition)
→
(Start condition)
→
(Read
of hour)
→
(Stop condition)
Assuming read was started at 05:59:59 P.M. and while reading seconds and minutes the time advanced to
06:00:00 P.M. At this time second digit is hold so the read as 05:59:59. Then the RS5C372A/B confirm (Stop
condition) and carry second digit being hold and the time changes to 06:00:00 P.M. Then, when the hour
digit is read, it changes to 6. The wrong results of 06:59:59 will be read.