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

Page 4

NXP Semiconductors

UM10301

 

User Manual PCF85x3, PCA8565 and PCF2123, PCA2125

2. Features

The NXP real-time clock portfolio includes types for low power, types for automotive and other high temperature applications and applications that need additional RAM. A third family of highly accurate temperature compensated real time clocks will be dealt with in a separate application note. Designed for a range of demanding applications, these real- time clocks/calendars are driven by a low-power 32.768 kHz quartz oscillator, use the SPI or I2C-bus for serial data transfer, and typically consume less than 1 μW of power.

Key features

•Oscillator requires 32.768 kHz external quartz crystal

•Resolution: seconds, minutes, hours, weekday, day, month, and year in 12- or 24-

hour (military) format. All time and alarm registers are in BCD format. Two types include a 1/10th and 1/100th second resolution register

•Clock operating voltage: 1.0 V to 5.5 V or wider, see Table 2

•Low backup current: Ranging from 100 nA to 2 μA at VDD = 1 V and Tamb = 25 °C

•Three line SPI with separate I/O or I2C serial interface

•Freely programmable timer and alarm functions, each with interrupt capability

•Freely programmable Watchdog timer

•Programmable clock output for peripheral devices: 32.768 kHz, 1024 Hz, 32 Hz and 1 Hz (not all types)

•One or two integrated oscillator capacitors (connected to the output of amplifier OSCO in case of only one integrated capacitor)

•Internal power-on reset

•Open-drain interrupt pin

•Wide variety of packages available including naked die

Addresses and data are transferred serially via an SPI bus with a maximum speed of 7.0 Mbps (PCF2123, PCA2125) or via a two-line, bidirectional I2C-bus that operates at a maximum speed of 400 kbps (Fast-Mode, PCF8563 and PCA8565) or 100 kbps (Standard-Mode, PCF8583 and PCF8593). The built-in word address register is incremented automatically after each data byte is written or read.

With the PCF8583, the address pin A0 is used to program the software address, so that two devices can be connected to the same I2C-bus without additional hardware.

Each RTC has an internal power-on reset and a programmable clock output with open drain configuration to drive peripheral devices. A low voltage detector (not included on the PCF8583,93 and PCA2125) warns if the integrity of all clock functions is no longer guaranteed.

Power consumption is kept to a minimum in all the devices. The PCF2123 and PCF8563, optimized for battery-powered applications, consume as little as 100 nA at 2V and 250 nA at 1V respectively. With careful selection of the crystal used, the PCF2123 consumes less than 100 nA on a 1.5 V supply.

The seconds, minutes, hours, days, weekdays, months, years as well as the minute alarm, hour alarm, day alarm and weekday alarm registers are all coded in Binary Coded Decimal (BCD) format. This format is popular with RTCs for the reason that time and date in BCD format can easily be displayed in human-readable style without conversion.

UM10301_1

 

© NXP B.V. 2008. All rights reserved.

User manual

Rev. 01 — 23 December 2008

4 of 52

Page 3 Page 5
Image 4
Page 3 Page 5
Contents Document information Info Content KeywordsAbstract Contact information NXP SemiconductorsRevision history Rev Date DescriptionIntroduction Features Register overview PCF8563 Address Register name BitEvent counter mode ComparisonFeatures Comparison of six real time clocksPower-on reset Power-on reset PORVoltage-low detector Voltage-low detection OscillatorOscillator-stop detection Pierce Oscillator equivalent diagram Overview of internal and external oscillator capacitorsOscillator frequency determining components UM10301 + C Typical values for crystal and surrounding capacitors Parameter Value Unit SourceUsing an external oscillator Oscillation allowanceCrystal and crystal selection Effect of temperature Modes which don’t work− f nom Capacitors and capacitor selection Accuracy Influences on time accuracy Oscillator tuning Oscillator tuning 10.1 PCF2123 Offset register Century and leap year, Daylight Saving Time Century trackingYear and leap year tracking Daylight Saving Time DSTInitialization of the RTC and setting the time Initialization and setting of alarm and timerBlock Diagram PCF8563 Alarm Setting the alarmBinary BCD Register Comments AddressAlarm function Setting the timer Setting the timerRegister Backup power supply Lithium Primary cellsBackup circuit using primary lithium cell Backup circuit using secondary cell NiCd or NiMH NiCd and NiMH secondary batteries13.3 Capacitors Charging the backup capacitor Diode selection Some suggestions for diode D11N4148 BAS716 BAS116 BAV170PCB layout guidelines PCB layout proposal for PCF8563 using leaded components Partial circuit switch down Hints to keep power consumption low Protection diodes0007 8473 ⋅ C b Rpmax as a function of bus capacitanceApplication diagram 1, I2C-bus interface Application diagram 2, SPI interfaceFirst period inaccuracy when using the timer Timer delaysTimer Source clock frequency Delay for n = General countdown timer behaviourFirst period delay for timer counter value n Timer source clock Minimum timer period Maximum timer periodTiming requirements for I2C read and write Block diagram I2C interface and Time counters I2C interfaceSequence of events example Read Troubleshooting Oscillator startup time Checking for oscillationNo communication via I2C-bus References Wrong time and date, wrong clock speedLegal information DefinitionsDisclaimers TrademarksContents
Top Page Image Contents