NXP Semiconductors PCA8565, PCF85x3, PCF2123, PCA2125 user manual Comparison, Event counter mode

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NXP Semiconductors

UM10301

 

User Manual PCF85x3, PCA8565 and PCF2123, PCA2125

The PCA8565 and PCA2125 oscillators operate over a wider temperature range (up to 125 ºC) and are suitable for use in the harsh environments found within automobiles. Power consumption remains low — only 700 nA at 2 V. Serial interface is I2C or SPI.

All the RTCs have ESD protection that exceeds 2000 V HBM per JESD22-A114, 200 V

MMper JESD22-A115. Charge Device Model values vary from 500 V to 2000 V CDM per JESD22-C101. Refer to the datasheet of the respective device. Latch-up testing, performed in accordance with JEDEC Standard JESD78, exceeds 100 mA.

3.Comparison

Table 2 on the next page gives a quick overview of the features, specifications and differences between the RTCs dealt with in this User Manual. The PCF8573 which belongs to the PCF85x3 family is no longer in production and has thus not been included in the table. However, this user manual is useful for this type as well.

Further there are some derived types from the main types listed in the table with small differences in for example delivery form or the number of integrated oscillator capacitors. Consult NXP for more details.

3.1 Event counter mode

Two real time clocks, PCF8583 and PCF8593, have an extraordinary feature. It is the event counter mode which can be selected by setting the appropriate bits in the control register. In this mode the oscillator is disabled and the oscillator input is switched to a high impedance state. This mode can be used to count pulses applied to the oscillator input OSCI. There is no crystal in the circuit and OSCO is left open circuit. The event counter stores up to 6 digits of data. Events are stored in BCD format. The 6 digits use three 8 bit registers (hundredth of a second, seconds, and minutes). D5 is the most significant and D0 the least significant digit. Every digit can contain values ranging from 0 to 9 and thus up to 999 999 events can be stored.

It is also possible to set an event counter alarm. When this function is enabled, the alarm occurs when the event counter registers match the programmed value. In this event the alarm flag is set. The inverted value of this flag can be transferred to the interrupt pin by setting the alarm interrupt enable in the alarm control register. In this mode the timer increments once for every one, one hundred, ten thousand or 1 million events, depending on the programmed value of the alarm control register. In all other events, the timer functions are as in clock mode.

Note that immediately following power-on, all internal registers are undefined and must be defined by software. It is also possible that upon power-on the device is initially in event-counter mode in which event the oscillator will not operate until the correct settings are written into the control registers.

The count value will increment on the falling edge. However, after a new count value has been programmed at least one rising edge must have occurred before events will be detected on the falling edge.

UM10301_1

 

© NXP B.V. 2008. All rights reserved.

User manual

Rev. 01 — 23 December 2008

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Contents Info Content Keywords Document informationAbstract Revision history Contact informationNXP Semiconductors Rev Date DescriptionIntroduction Features Register overview PCF8563 Address Register name BitEvent counter mode ComparisonFeatures Comparison of six real time clocksPower-on reset POR Power-on resetVoltage-low detector Oscillator Voltage-low detectionOscillator-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 Year and leap year tracking Century and leap year, Daylight Saving TimeCentury tracking Daylight Saving Time DSTInitialization and setting of alarm and timer Initialization of the RTC and setting the timeBlock Diagram PCF8563 Binary BCD AlarmSetting the alarm 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 1N4148 Diode selectionSome suggestions for diode D1 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 interfaceTimer Source clock frequency Delay for n = First period inaccuracy when using the timerTimer delays 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 speedDisclaimers Legal informationDefinitions TrademarksContents
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