Datasheet

PCF2127AT All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
Product data sheet Rev. 6 — 11 July 2013 33 of 86
NXP Semiconductors
PCF2127AT
Integrated RTC, TCXO and quartz crystal
After this read/write access is completed, the time circuit is released again. Any pending
request to increment the time counters that occurred during the read/write access is
serviced. A maximum of 1 request can be stored; therefore, all accesses must be
completed within 1 second (see Figure 18
).
As a consequence of this method, it is very important to make a read or write access in
one go, that is, setting or reading seconds through to years should be made in one single
access. Failing to comply with this method could result in the time becoming corrupted.
As an example, if the time (seconds through to hours) is set in one access and then in a
second access the date is set, it is possible that the time may increment between the two
accesses. A similar problem exists when reading. A roll-over may occur between reads
thus giving the minutes from one moment and the hours from the next. Therefore it is
advised to read all time and date registers in one access.
Fig 17. Data flow of the time function
Fig 18. Access time for read/write operations
001aaf901
1 Hz tick
12_24 hour mode
WEEKDAY
SECONDS
MINUTES
HOURS
DAYS
LEAP YEAR
CALCULATION
MONTHS
YEARS
t < 1 s
013aaa215
SLAVE ADDRESS DATA STOPDATA
START