Datasheet
PCF2129 All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2014. All rights reserved.
Product data sheet Rev. 7 — 19 December 2014 30 of 86
NXP Semiconductors
PCF2129
Accurate RTC with integrated quartz crystal for industrial applications
8.8.7 Register Years
8.8.8 Setting and reading the time
Figure 15 shows the data flow and data dependencies starting from the 1 Hz clock tick.
During read/write operations, the time counting circuits (memory locations 03h through
09h) 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. 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 16
).
Table 36. Years - years register (address 09h) bit allocation
Bits labeled as X are undefined at power-on and unchanged by subsequent resets.
Bit 7 6 5 4 3 2 1 0
Symbol YEARS (0 to 99)
Reset
value
XXXXXXXX
Table 37. Years - years register (address 09h) bit description
Bits labeled as X are undefined at power-on and unchanged by subsequent resets.
Bit Symbol Value Place value Description
7 to 4 YEARS 0 to 9 ten’s place actual year coded in BCD format
3to0 0to9 unit place
Fig 15. Data flow of the time function
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