pca2125 NXP Semiconductors, pca2125 Datasheet - Page 5

• Manufacturer Part Number: pca2125
• Description: Spi Real Time Clock / Calendar Semiconductors
• Manufacturer: NXP Semiconductors

NXP Semiconductors
6. Functional description
PCA2125_00
Preliminary data sheet
The PCA2125 contains sixteen 8-bit registers with an auto-incrementing address register,
and on-chip 32.768 kHz oscillator with one integrated capacitor, a frequency divider which
provides the source clock for the Real Time Clock (RTC), a programmable clock output,
and an 8 MHz SPI.
All sixteen registers are designed as addressable 8-bit parallel registers although not all
bits are implemented. 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). Addresses 09H through 0CH define the alarm
condition, whilst address 0DH defines the clock out mode.
The seconds, minutes, hours, days, weekdays, months and years registers are all coded
in BCD format. When one of the RTC registers is read the contents of all counters are
frozen. Therefore, faulty reading of the clock/calendar during a carry condition is
prevented.
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 less than 1ms to more than 4hours. There are also two pre-defined timers
which can be used to generate an interrupt once per second or once per minute, but these
are defined at address 01H.
Table 4:
Timer source clock
4096 Hz
64 Hz
1 Hz
1⁄60 Hz
Countdown timer durations
Rev. 00.11 — 30 January 2007
minimum timer duration
244 µs
15.625 ms
1 s
60 s
SPI Real time clock / calendar
maximum timer duration
62.256 ms
3.984 s
255 s
4 hrs 15 minutes
PCA2125
© NXP B.V. 2007. All rights reserved.
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