NXP Semiconductors | UM10301 |
| User Manual PCF85x3, PCA8565 and PCF2123, PCA2125 |
Fig 22. Sequence of events (example READ)
From this follows:
•A I2C read must be terminated within one second of initiation;
•The RTC will automatically terminate the read if it remains active for longer than one second;
•Each time auto termination occurs, the RTC looses one second;
•The signal BLOCK is also active during a write. A write must also last less than one second;
•BLOCK is necessary for a write since the registers must not update whilst new data
is being written. That is impossible anyway, since the clock is switched from the 1 Hz clock to the internal I2C clock.
Remark: The RTCs allow to set the word address in order to address a particular register, for example the seconds register. If the application software is written such that separate bus accesses are used to read the individual time/date registers it is possible that after reading/writing those registers the time as read or written by the system controller is not correct. This is because time counter freeze – implemented to avoid such errors - is active only during one access, starting from the START condition and ending when the STOP condition occurs. Now still the errors mentioned in the introduction of this
UM10301_1 |
| © NXP B.V. 2008. All rights reserved. |
User manual | Rev. 01 — 23 December 2008 | 47 of 52 |
