NXP Semiconductors
PCF8564A
Real time clock and calendar
8.4.7 Register Years
Table 17. Years - years register (08h) bit description
Bit Symbol
Value Place value Description
7 to 4 YEARS
0 to 9
ten’s place actual year coded in BCD format[1]
3 to 0
0 to 9
unit place
[1] When the register Years overflows from 99 to 00, the century bit C in the register Months is toggled.
The PCF8564A compensates for leap years by adding a 29th day to February if the year
counter contains a value which is divisible by 4, including the year 00.
8.5 Setting and reading the time
Figure 6 shows the data flow and data dependencies starting from the 1 Hz clock tick.
1 Hz tick
SECONDS
MINUTES
LEAP YEAR
CALCULATION
HOURS
DAYS
WEEKDAY
MONTHS
YEARS
C
013aaa092
Fig 6. Data flow for the time function
During read/write operations, the time counting circuits (memory locations 02h through
08h) are blocked.
This prevents
• Faulty writing or 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 access, is
serviced. A maximum of 1 request can be stored; therefore, all accesses must be
completed within 1 second (see Figure 7).
PCF8564A
Product data sheet
All information provided in this document is subject to legal disclaimers.
Rev. 02 — 30 September 2010
© NXP B.V. 2010. All rights reserved.
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