Micro Crystal

Real Time Clock / Calendar Module

RV-8564

19/40

During read / write operations, the time counting circuits (memory locations 02h through 08h) are blocked, in order

to prevent the following:

•

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.

As a consequence of this method, it is very important to make a read or write access in one go. This means, setting

or reading seconds through 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 hours) is set in one access, and then, in a second access the date is

set, it is possible that the time may be incremented 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.

Recommended method for reading the time:

1. Send a START condition and the slave address for write (A2h)

2. Set the address pointer to 2 (seconds) by sending 02h

3. Send a RE-START condition or STOP followed by START

4. Send the slave address for read (A3h)

5. Read the seconds

6. Read the minutes

7. Read the hours

8. Read the days

9. Read the weekdays

10. Read the century and months

11. Read the years

12. Send a STOP condition