pcf2127a NXP Semiconductors, pcf2127a Datasheet - Page 5

• Manufacturer Part Number: pcf2127a
• Description: Integrated Rtc, Tcxo And Quartz Crystal
• Manufacturer: NXP Semiconductors

NXP Semiconductors
8. Functional description
PCF2127A_1
Product data sheet
8.1 Register overview
The PCF2127A is a Real Time Clock (RTC) and calendar with an on-chip Temperature
Compensated Crystal 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 PCF2127A contains 30 8-bit registers, that are used for many different functions,
such as clock, alarm, watchdog, timer, timestamp etc. (see
The PCF2127A has an output reset pin: the output reset is activated on Power-On Reset
(POR), and whenever the oscillator is stopped (see
The PCF2127A features 512 bytes of general purpose static RAM, which is battery
backed and can be used independent of the RTC functionality (see
The PCF2127A 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 certain threshold value, a flag is set to indicate that the
battery must be replaced. This can be used to ensure the integrity of the data during
periods of battery backup.
A power failure detection circuit monitors the voltage of the power fail input pin PFI. When
the voltage on the power fail input pin PFI goes below an internal reference (1.25 V), the
power fail output pin PFO is activated (see
The PCF2127A contains 30 8-bit registers (see
address register: the register address will be incremented automatically after each read or
write data byte up to the register 1Bh. After register 1Bh the auto-incrementing will wrap
around to address 00h. The registers 1Ch and 1Dh must be addressed directly (see
Figure
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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
3).
Section
Rev. 01 — 21 January 2010
8.2).
Section
Integrated RTC, TCXO and quartz crystal
Table
Section
8.6.4).
Section
4) with an auto-incrementing
8.6.1). Accurate timekeeping is
Section
Section
8.7).
Section
9). The maximum speed
PCF2127A
8.1).
Section
Section
8.10).
Section
© NXP B.V. 2010. All rights reserved.
8.5).
8.6.3). When
8.9).
2
C-bus or
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