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R2045S Datasheet(PDF) 26 Page - RICOH electronics devices division |
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R2045S Datasheet(HTML) 26 Page - RICOH electronics devices division |
26 / 50 page R2045S/D 26 • 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 R2045S/D 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. CE Time counts within RTC 14:00:01 Actual time 13:59:59 Max.62 µs 14:00:00 13:59:59 14:00:00 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 31 µs 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 62 µs 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. |
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