Nxp Semiconductors PCA2125 User Manual

 

 

UM10301_1 

© NXP B.V. 2008. All rights reserved.

 

 

From this follows: 

• A I

2

C 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 I

2

C clock. 

 

: 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