NXP Semiconductors PCA2125, PCF85x3, PCF2123, PCA8565 user manual Sequence of events example Read

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NXP Semiconductors

UM10301

 

User Manual PCF85x3, PCA8565 and PCF2123, PCA2125

Fig 22. Sequence of events (example READ)

From this follows:

A I2C 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 I2C clock.

Remark: 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

UM10301_1

 

© NXP B.V. 2008. All rights reserved.

User manual

Rev. 01 — 23 December 2008

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Contents Abstract Info Content KeywordsDocument information Rev Date Description Contact informationNXP Semiconductors Revision historyIntroduction Features Address Register name Bit Register overview PCF8563Comparison Event counter modeComparison of six real time clocks FeaturesVoltage-low detector Power-on reset PORPower-on reset Oscillator-stop detection OscillatorVoltage-low 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 Daylight Saving Time DST Century and leap year, Daylight Saving TimeCentury tracking Year and leap year trackingBlock Diagram PCF8563 Initialization and setting of alarm and timerInitialization of the RTC and setting the time Register Comments Address AlarmSetting the alarm Binary BCDAlarm function Register Setting the timerSetting the timer 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 BAS716 BAS116 BAV170 Diode selectionSome suggestions for diode D1 1N4148PCB 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 interfaceGeneral countdown timer behaviour First period inaccuracy when using the timerTimer delays Timer Source clock frequency Delay for n =Timer 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 ReferencesTrademarks Legal informationDefinitions DisclaimersContents