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PDF PCF2129A Data sheet ( Hoja de datos )
| Número de pieza | PCF2129A | |
| Descripción | Integrated RTC TCXO and quartz crystal | |
| Fabricantes | NXP Semiconductors | |
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PCF2129A
Integrated RTC, TCXO and quartz crystal
Rev. 01 — 13 January 2010
www.DataSheet4U.com
Product data sheet
1. General description
The PCF2129A is a CMOS1 real time clock and calendar with an integrated Temperature
Compensated Crystal (Xtal) Oscillator (TCXO) and a 32.768 kHz quartz crystal optimized
for very high accuracy and very low power consumption. The PCF2129A has a selectable
I2C-bus or SPI-bus, a backup battery switch-over circuit, a programmable watchdog
function, a timestamp function, and many other features.
2. Features
Temperature Compensated Crystal Oscillator (TCXO) with integrated capacitors
Accuracy: ±3 ppm from −15 °C to +60 °C
Integration of a 32.768 kHz quartz crystal and oscillator in the same package
Provides year, month, day, weekday, hours, minutes, and seconds
Timestamp function
with interrupt capability
detection of two different events on one multilevel input pin (e.g. for tamper
detection)
Two line bidirectional 1 MHz Fast-mode Plus (Fm+) I2C-bus interface (IOL = 20 mA at
pin SDA)
3 line SPI-bus with separate data input and output (maximum speed 6.5 Mbit/s)
Battery backup input pin and switch-over circuitry
Battery backed output voltage pin
Battery low detection function
Extra power fail detection function with input and output pins
Power-On Reset Override (PORO)
Oscillator stop detection function
Interrupt output (open-drain)
Programmable 1 second or 1 minute interrupt
Programmable watchdog timer with interrupt and reset capability
Programmable alarm function with interrupt capability
Programmable square wave open-drain output pin
Clock operating voltage: 1.2 V to 4.2 V
Low supply current: typical 0.65 μA at VDD = 3.0 V and Tamb = 25 °C
Automatic leap year correction
1. The definition of the abbreviations and acronyms used in this data sheet can be found in Section 17.
1 page  
NXP Semiconductors
PCF2129A
Integrated RTC, TCXwOwwa.nDdatqauShaeretzt4cUr.cyosmtal
8. Functional description
The PCF2129A is a Real Time Clock and calendar (RTC) with an on-chip Temperature
Compensated crystal (Xtal) Oscillator (TCXO) and a 32.768 kHz quartz crystal integrated
into the same package.
Address and data are transferred by a selectable 1 MHz Fast-mode Plus (Fm+) I2C-bus or
a 3 line SPI-bus with separate data input and output (see Section 9). The maximum speed
of the SPI-bus is 6.5 Mbit/s.
The PCF2129A contains 28 8-bit registers, that are used for many different functions,
such as clock, alarm, watchdog, timestamp etc. (see Section 8.1).
The PCF2129A has a backup battery input pin and backup battery switch-over circuit
which monitors the main power supply and automatically switches to the backup battery
when a power failure condition is detected (see Section 8.5.1). Accurate timekeeping is
maintained even when the main power supply is interrupted.
A battery low detection circuit monitors the status of the battery (see Section 8.5.3). When
the battery voltage goes below a threshold value, a flag is set to indicate that the battery
must be replaced soon. This ensures the integrity of the data during periods of battery
backup.
8.1 Register overview
The PCF2129A contains 28 8-bit registers (see Table 4) with an auto-incrementing
address register: the built-in address register will increment automatically after each read
or write of a data byte up to the register 1Bh. After register 1Bh the auto-incrementing will
wrap around to address 00h.
• The first three registers (memory address 00h, 01h, and 02h) are used as control
registers (see Section 8.2).
• The memory addresses 03h through to 09h are used as counters for the clock
function (seconds up to years). The date is automatically adjusted for months with
fewer than 31 days, including corrections for leap years. The clock can operate in
12-hour mode with an AM/PM indication or in 24-hour mode (see Section 8.8).
• Addresses 0Ah through 0Eh define the alarm function. It can be selected that an
interrupt is generated when an alarm event occurs (see Section 8.9).
• The register 0Fh defines the temperature measurement period and the clock out
mode. The temperature measurement can be selected from every 4 minutes (default)
down to every 30 seconds (see Table 9). CLKOUT frequencies of 32.768 kHz
(default) down to 1 Hz for use as a system clock, a microcontroller clock etc. can be
chosen (see Section 8.3.2).
• Address registers 10h and 11h are used for the watchdog timer functions. The
watchdog timer has four selectable source clocks allowing for timer periods from less
than 1 ms to greater than 4 hours. An interrupt will be generated when the watchdog
times out.
• Address registers 12h to 18h are used for the timestamp function. When the trigger
event happens, the actual time is saved in the timestamp registers (see Section 8.11).
• Address register 19h is used for the correction of the crystal aging effect (see
Section 8.4.1).
PCF2129A_1
Product data sheet
Rev. 01 — 13 January 2010
© NXP B.V. 2010. All rights reserved.
5 of 68
5 Page 
NXP Semiconductors
PCF2129A
Integrated RTC, TCXwOwwa.nDdatqauShaeretzt4cU.rcyosmtal
8.3 Register CLKOUT_ctl
Table 8. CLKOUT_ctl - CLKOUT control register (address 03h) bit description
Bit Symbol
Value
Description
7 to 6 TCR[1:0]
see Table 9 temperature measurement period
5 to 3 -
- unused
2 to 0 COF[2:0]
see Table 10 CLKOUT frequency selection
8.3.1 Temperature compensated crystal oscillator
The frequency of tuning fork quartz crystal oscillators are temperature-dependent. In the
PCF2129A the frequency drift caused by temperature variation is corrected by adjusting
the load capacitance of the crystal oscillator.
The load capacitance is changed by switching between two load capacitance values using
a modulation signal with a programmable duty cycle. Every chip is calibrated in order to
produce, at the measured temperature, the correct duty cycle which compensates for the
frequency shift.
The frequency accuracy can be evaluated by measuring the frequency of the square
wave signal available at the output pin CLKOUT. However, the selection of
fCLKOUT = 32.768 kHz (default value) leads to inaccurate measurements. The most
accurate frequency measurement occurs when fCLKOUT = 1 Hz is selected (see Table 10).
8.3.1.1 Temperature measurement
The PCF2129A has a temperature sensor circuit used to perform the temperature
compensation of the frequency. The temperature is measured immediately after power-on
and then periodically with a period set by the temperature conversion rate TCR[1:0] in the
register CLKOUT_ctl.
Table 9. Temperature measurement period
TCR[1:0]
Temperature measurement period
00 [1] 4 min
01 2 min
10 1 min
11 30 seconds
[1] Default value.
8.3.2 Clock output
A programmable square wave is available at pin CLKOUT. Operation is controlled by the
COF control bits in register CLKOUT_ctl. Frequencies of 32.768 kHz (default) down to
1 Hz can be generated for use as a system clock, microcontroller clock, input to a charge
pump, or for calibration of the oscillator.
CLKOUT is an open-drain output and enabled at power-on. When disabled, the output is
high-impedance.
The duty cycle of the selected clock is not controlled, however, due to the nature of the
clock generation, all but the 32.768 kHz frequencies will be 50 : 50.
PCF2129A_1
Product data sheet
Rev. 01 — 13 January 2010
© NXP B.V. 2010. All rights reserved.
11 of 68
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