Real Time Clock; Rtc Backup Battery Charging; Security - Nokia NSB-6 Series Technical Documentation Manual

PAMS Technical Documentation
quadrature signals. A slow speed digital to analogue converter will pro-
vide automatic frequency control (AFC).
COBBA is at any time connected to MAD asic with two interfaces, one for
transferring TX and RX data between MAD and COBBA and one for
transferring codec RX/TX samples.

Real Time Clock

Requirements for a real time clock implementation are a basic clock
(hours and minutes), a calender and a timer with alarm and power on/off
–function and miscellaneous calls. The RTC will contain only the time
base and the alarm timer but all other functions (e.g. calendar) will be im-
plemented with the MCU software. The RTC needs a power backup to
keep the clock running when the phone battery is disconnected. The
backup power is supplied from a rechargable polyacene battery that can
keep the clock running some ten minutes. If the backup has expired, the
RTC clock restarts after the main battery is connected. The CCONT
keeps MCU in reset until the 32kHz source is settled (1s max).
The CCONT is an ideal place for an integrated real time clock as the asic
already contains the power up/down functions and a sleep control with
the 32kHz sleep clock, which is running always when the phone battery is
connected. This sleep clock is used for a time source to a RTC block.

RTC backup battery charging

CHAPS has a current limited voltage regulator for charging a backup bat-
tery. The regulator derives its power from VOUT so that charging can take
place without the need to connect a charger. The backup battery is only
used to provide power to a real time clock when VOUT is not present so it
is important that power to the charging circuitry is derived from VOUT and
that the charging circuitry does not present a load to the backup battery
when VOUT is not present.
It should not be possible for charging current to flow from the backup bat-
tery into VOUT if VOUT happens to be lower than VBACK. Charging cur-
rent will gradually diminish as the backup battery voltage reaches that of
the regulation voltage.

Security

The phone flash program and IMEI code are software protected using an
external security device that is connected between the phone and a PC.
The security device uses the phone given IMEI number, the software ver-
sion number and a 24bit hardware random serial number that is read
from the COBBA and calculates a flash authority identification number
that is stored into the phone (emulated) EEPROM.
Issue 1 06/2000
E Nokia Mobile Phones Ltd.
NSB–6
System Module
Page 37