PCF2123U/12(2011) Ver la hoja de datos (PDF) - NXP Semiconductors.
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PCF2123U/12 Datasheet PDF : 63 Pages
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NXP Semiconductors
PCF2123
SPI Real time clock/calendar
During read/write operations, the time counting circuits (memory locations 02h through
08h) are blocked.
This prevents
• Faulty reading of the clock and calendar during a carry condition
• Incrementing the time registers during the read cycle
After this read/write access is completed, the time circuit is released again and 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 11).
t<1s
data bus
COMMAND
DATA
DATA
DATA
chip enable
013aaa222
Fig 11. Access time for read/write operations
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.
PCF2123
Product data sheet
All information provided in this document is subject to legal disclaimers.
Rev. 5 — 27 April 2011
© NXP B.V. 2011. All rights reserved.
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