Nxp Semiconductors PCF2123 User Manuals

Table of 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