NXP Semiconductors PCF2123 user manual Document information, Info Content Keywords, Abstract

Page 1

UM10301

User Manual for NXP Real Time Clocks PCF85x3, PCA8565 and PCF2123, PCA2125

Rev. 01 — 23 December 2008

User manual

Document information

Info	Content

Keywords	PCF8563, PCF8573, PCF8583, PCF8593, PCA8565, PCF2123,
	PCA2125, PCF2120, RTC, real time clock, timekeeping, crystal,
	32.768 kHz, backup.

Abstract	This application note aims to assist a user of above mentioned Real Time
	Clocks in achieving succesful design-in and application. It contains useful
	hints with respect to electrical schematic and PCB layout as well as code
	examples for the well established NXP PCF8563 and related Real Time
	Clocks. Also the more recent Real Time Clocks PCF2123 and PCA2125
	have been taken into account.

Image 1

Contents Document information Info Content KeywordsAbstract NXP Semiconductors Contact informationRevision history Rev Date DescriptionIntroduction Features Address Register name Bit Register overview PCF8563Comparison Event counter modeComparison of six real time clocks FeaturesPower-on reset Power-on reset PORVoltage-low detector Voltage-low detection OscillatorOscillator-stop detection Overview of internal and external oscillator capacitors Pierce Oscillator equivalent diagramOscillator frequency determining components UM10301 + C Parameter Value Unit Source Typical values for crystal and surrounding capacitorsOscillation allowance Using an external oscillatorCrystal and crystal selection Modes which don’t work Effect of temperature− f nom Capacitors and capacitor selection Accuracy Influences on time accuracy Oscillator tuning Oscillator tuning 10.1 PCF2123 Offset register Century tracking Century and leap year, Daylight Saving TimeYear and leap year tracking Daylight Saving Time DSTInitialization of the RTC and setting the time Initialization and setting of alarm and timerBlock Diagram PCF8563 Setting the alarm AlarmBinary BCD Register Comments AddressAlarm function Setting the timer Setting the timerRegister Lithium Primary cells Backup power supplyBackup circuit using primary lithium cell NiCd and NiMH secondary batteries Backup circuit using secondary cell NiCd or NiMH13.3 Capacitors Charging the backup capacitor Some suggestions for diode D1 Diode selection1N4148 BAS716 BAS116 BAV170PCB layout guidelines PCB layout proposal for PCF8563 using leaded components Partial circuit switch down Protection diodes Hints to keep power consumption low0007 Rpmax as a function of bus capacitance 8473 ⋅ C bApplication diagram 2, SPI interface Application diagram 1, I2C-bus interfaceTimer delays First period inaccuracy when using the timerTimer Source clock frequency Delay for n = General countdown timer behaviourTimer source clock Minimum timer period Maximum timer period First period delay for timer counter value nTiming requirements for I2C read and write I2C interface Block diagram I2C interface and Time countersSequence of events example Read Oscillator startup time Checking for oscillation TroubleshootingNo communication via I2C-bus Wrong time and date, wrong clock speed ReferencesDefinitions Legal informationDisclaimers TrademarksContents