PCA8565 All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2014. All rights reserved.
Product data sheet Rev. 4 — 5 December 2014 12 of 48
NXP Semiconductors
PCA8565
Real time clock/calendar
8.4.7 Register Years
8.5 Setting and reading the time
Figure 5 shows the data flow and data dependencies starting from the 1 Hz clock tick.
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 access is
serviced. A maximum of 1 request can be stored; therefore, all accesses must be
completed within 1 second (see Figure 6
).
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.
Table 18. Register Years (08h) bits description
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 5. Data flow for the time function
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