CBC34123 EnerChip™ RTC

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DS-72-31 V.08

Page 5 of 9

Preliminary

Functional Description of Integrated PCF2123 Real-Time Clock

The PCF2123 contains 16 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 16 registers are designed as addressable 8-bit parallel registers although not all bits are implemented.

registers Seconds, Minutes, Hours, Days, Weekdays, Months, and Years are all coded in Binary Coded

Decimal (BCD) format. When one of the RTC registers is written or read the contents of all counters are

frozen. Therefore, faulty writing or reading of the clock and calendar during a carry condition is prevented.

selectable source clocks allowing for countdown periods in the range from 244 ms 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).

Low Power Operation

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

Power Consumption with Respect to Quartz Series Resistance

The series resistance acts as a loss element. Low R

Important Reference Documents

For complete specifications of the integrated PCF2123 Real-Time Clock, see here:

http://www.nxp.com/documents/data_sheet/PCF2123.pdf .

For complete specifications of the Cymbet 5µAh EnerChip and integrated power management circuit, see here:

http://www.cymbet.com/pdfs/DS-72-21.pdf .

The EnerChip and power management functions within the CBC34123 are configured as in Mode 1 (VMODE =

GND) described in the CBC3105 data sheet.

For guidelines regarding crystal selection and other important information pertaining to the PCF2123, see the

UM10301 - User Manual for NXP Real Time Clocks, located here:

http://www.nxp.com/documents/user_manual/UM10301.pdf