PCF2123BS NXP [NXP Semiconductors], PCF2123BS Datasheet - Page 6

• Manufacturer Part Number: PCF2123BS
• Description: SPI Real time clock/calendar
• Manufacturer: NXP [NXP Semiconductors]

NXP Semiconductors
9. Functional description
PCF2123_1
Product data sheet
9.1 Low power operation
The PCF2123 contains sixteen 8-bit registers with an auto-incrementing address counter,
an on-chip 32.768 kHz oscillator with two integrated load capacitors, a frequency divider
which provides the source clock for the Real Time Clock (RTC), a programmable clock
output, and a 6.25 Mbit/s SPI-bus. An offset register allows fine tuning of the clock.
All sixteen registers are designed as addressable 8-bit parallel registers although not all
bits are implemented.
Minimum power operation will be achieved by reducing the number and frequency of
switching signals inside the IC, i.e. low frequency timer clocks and a low frequency
CLKOUT will result in lower operating power. A second prime consideration is the series
resistance R
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The first two registers (memory address 00h and 01h) are used as control registers.
The memory addresses 02h through 08h are used as counters for the clock function
(seconds up to years). The Seconds, Minutes, Hours, Days, Weekdays, Months and
Years registers are all coded in Binary Coded Decimal (BCD) format. When one of the
RTC registers is read the contents of all counters are frozen. Therefore, faulty reading
of the clock and calendar during a carry condition is prevented.
Addresses 09h through 0Ch define the alarm condition.
Address 0Dh defines the offset calibration.
Address 0Eh defines the clock out and timer mode.
Address registers 0Eh and 0Fh are used for the countdown timer function. The
countdown timer has four selectable source clocks allowing for countdown periods in
the range from 244 s up to four hours. There are also two pre-defined timers which
can be used to generate an interrupt once per second or once per minute. These are
defined in register Control_2 (01h).
s
of the quartz used.
Rev. 01 — 19 November 2008
SPI Real time clock/calendar
PCF2123
© NXP B.V. 2008. All rights reserved.
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