RX5C348A Datasheet, PDF (25/45 Pages) RICOH electronics devices division – 4-WIRE SERIAL INTERFACE

Rx5C348A/B
Considerations in Reading and Writing Time Data under special condition
Any carry to the second digits in the process of reading or writing time data may cause reading or writing
erroneous time data. For example, suppose a carry out of 13:59:59 into 14:00:00 occurs in the process of
reading time data in the middle of shifting from the minute digits to the hour digits. At this moment, the second
digits, the minute digits, and the hour digits read 59 seconds, 59 minutes, and 14 hours, respectively (indicating
14:59:59) to cause the reading of time data deviating from actual time virtually 1 hour. A similar error also
occurs in writing time data. To prevent such errors in reading and writing time data, the Rx5C348A/B has the
function of temporarily locking any carry to the second digits during the high interval of the CE pin and unlocking
such a carry in its high to low transition. Note that a carry to the second digits can be locked for only 1 second,
during which time the CE pin should be driven low.
Actual time
CE
Time counts
within RTC
13:59:59
13:59:59
14:00:00
Max.62µs
14:00:00
14:00:01
14:00:01
The effective use of this function requires the following considerations in reading and writing time data:
(1) Hold the CE pin high in each session of reading or writing time data.
(2) Ensure that the high interval of the CE pin lasts within 1 second. Should there be any possibility of the host
going down in the process of reading or writing time data, make arrangements in the peripheral circuitry as to
drive the CE pin low or open at the moment that the host actually goes down.
(3) Leave a time span of 31µs or more from the low to high transition of the CE pin to the start of access to
addresses 0h to 6h in order that any ongoing carry of the time digits may be completed within this time span.
(4) Leave a time span of 62µs or more from the high to low transition of the CE pin to its low to high transition in
order that any ongoing carry of the time digits during the high interval of the CE pin may be adjusted within this
time span.
The considerations listed in (1), (3), and (4) above are not required when the process of reading or writing time
data is obviously free from any carry of the time digits.
(e.g. reading or writing time data in synchronization with the periodic interrupt function in the level mode or the
alarm interrupt function).
Good and bad examples of reading and writing time data are illustrated on the next page.
Rev.2.01
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