RV5C339A_03 Datasheet, PDF (25/46 Pages) RICOH electronics devices division – 3-WIRE SERIAL INTERFACE REAL-TIME CLOCK IC WITH VOLTAGE MONITORING FUNCTION

RV5C339A
1.5 Considerations in Reading and Writing Time Data
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 RV5C339A has the function of temporarily locking any
carry of the time digits during the high interval of the CE pin and unlocking such a carry in its high to low transition.
Note that a carry of 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 real-time clocks
13:59:59
13:59:59
14:00:00
MAX.61µs
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 address-
es 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 61µs 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.
(5) 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.
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