PCF2129AT NXP [NXP Semiconductors], PCF2129AT Datasheet - Page 5

• Manufacturer Part Number: PCF2129AT
• Description: Integrated RTC, TCXO and quartz crystal
• Manufacturer: NXP [NXP Semiconductors]

NXP Semiconductors
8. Functional description
PCF2129A_1
Product data sheet
8.1 Register overview
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+) I
a 3 line SPI-bus with separate data input and output (see
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
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
maintained even when the main power supply is interrupted.
A battery low detection circuit monitors the status of the battery (see
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.
The PCF2129A contains 28 8-bit registers (see
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.
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The first three registers (memory address 00h, 01h, and 02h) are used as control
registers (see
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
Addresses 0Ah through 0Eh define the alarm function. It can be selected that an
interrupt is generated when an alarm event occurs (see
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
(default) down to 1 Hz for use as a system clock, a microcontroller clock etc. can be
chosen (see
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
Address register 19h is used for the correction of the crystal aging effect (see
Section
8.4.1).
Section
Section
Rev. 01 — 13 January 2010
8.3.2).
8.2).
Table
9). CLKOUT frequencies of 32.768 kHz
Integrated RTC, TCXO and quartz crystal
Section
Table
Section
4) with an auto-incrementing
8.5.1). Accurate timekeeping is
Section
Section
8.1).
9). The maximum speed
PCF2129A
Section
8.9).
Section
© NXP B.V. 2010. All rights reserved.
Section
8.5.3). When
8.8).
2
C-bus or
5 of 68
8.11).