Preliminary
CBC34123 EnerChip™ RTC
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
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.
•
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
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.
•
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 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
s
of the quartz used.
Power Consumption with Respect to Quartz Series Resistance
The series resistance acts as a loss element. Low R
S
will reduce current consumption further.
DS-72-31 V.08
©2012 Cymbet Corporation • Tel: +1-763-633-1780 • www.cymbet.com
Page 5 of 9
CYMBET [ CYMBET CORPORATION ]
