Three application notes are available for NXP’s real time clocks. AN108527 discusses soldering and application configuration information for the PCF2127A and PCF2129A. UM10301 is a very extensive user manual covering all application aspects of the PCF85x3, PCA8565, PCF2123, and PCA21125 real time clocks. AN10652 deals with software implementation of temperature compensation for the PCF8563 and related type products.