NXP Semiconductors PCF85x3, PCF2123, PCA8565, PCA2125 user manual Contents

NXP Semiconductors	UM10301
	User Manual PCF85x3, PCA8565 and PCF2123, PCA2125

22. Contents

1.	Introduction	3
2.	Features	4
3.	Comparison	6
3.1	Event counter mode	6
4.	Power-on reset (POR)	8
5.	Voltage-low detector	8
6.	Oscillator	9
6.1	Oscillation allowance	15
6.2	Using an external oscillator	15
7.	Crystal and crystal selection	16
7.1	Modes which don’t work	17
7.2	Effect of temperature	17
8.	Capacitors and capacitor selection	19
9.	Accuracy	20
10.	Oscillator tuning	22
10.1	PCF2123 Offset register	24

11.Century and leap year, Daylight Saving Time.25

11.1	Century tracking	25
11.2	Year and leap year tracking	25
11.3	Daylight Saving Time (DST)	25
12.	Initialization and setting of alarm and timer....	26
12.1	Initialization of the RTC and setting the time ....	26
12.2	Alarm	27
12.3	Setting the timer	29
13.	Backup power supply	30
13.1	Lithium Primary cells	30
13.2	NiCd and NiMH secondary batteries	32
13.3	Capacitors	33
13.3.1	Charging the backup capacitor	34
13.3.2	Estimation of backup time with capacitor	34
13.4	Diode selection	35
14.	PCB layout guidelines	36
15.	Partial circuit switch down	38
16.	Hints to keep power consumption low	39

17.First period inaccuracy when using the timer 43

18.	Timing requirements for I2C read and write ....	45
19.	Troubleshooting	48
19.1	Oscillator startup time	48
19.2	Checking for oscillation	48
19.3	No communication via I2C-bus	49
19.4	Wrong time and date, wrong clock speed	50
20.	References	50

21.	Legal information	51
21.1	Definitions	51
21.2	Disclaimers	51
21.3	Trademarks	51
22.	Contents	52

Please be aware that important notices concerning this document and the product(s) described herein, have been included in the section 'Legal information'.

© NXP B.V. 2008. All rights reserved.

For more information, please visit: http://www.nxp.com

For sales office addresses, email to: salesaddresses@nxp.com

Date of release: 23 December 2008

Document identifier: UM10301_1