Motorola GP Series Detailed Service Manual page 130

1-18
8.2.2 Digital Architecture
MCU Configuration
There is one common MCU architecture for low-tier as well as for the high-tier products. It covers the
Conventional and Trunking portables. An open architecture system with the new HC11FL0 as the
processor is used. Combinations of different size RAM, ROM and EEPROM are available for various
application software.
REAL TIME CLOCK (RTC)
This radio supports Real Time Clock (RTC) module for purposes of Message Time Stamping and
Time Keeping. The RTC module resides in the micro-processor HC11FL0. It is kept alive by a back-
up Lithium Ion battery when the primary battery is removed.
HC11FL0
MODA
MODB
PI6
R420
PI7
Circuit Description
The RTC module which resides in the HC11FL0 is powered by the ModB/Vstby pin and PI6/PI7 form
the crystal oscillator circuit. Clock frequency of 38.4kHz from a crystal oscillator provides the
reference signal. In the processor, the frequency is divided down to 1Hz.
As the RTC module is powered separately from the processor Vdd, the RTC is kept alive through the
ModB / Vstby pin when the radio is switched off. A small button Lithium Ion battery continues to feed
the RTC when the primary battery is removed.
A MOSFET Q416 switches in the LiO supply when Vdd is removed. Q416 also provides isolation
from BOOT_CTRL function in the event of radio program flashing. A small 3.3V regulator is used to
charge the LiO battery.
FL401 C436
OUT
38.4kHz
GND
IN
R426
C437
Figure 1-11: RTC Circuit
Vddd
R461 C435
CR411
1
Q416
2
3 2
1
R462
R463
CR413
300
5
4
Q417
3
1
6
2
UNSWB+ SWB+
3
4
THEORY OF OPERATION
UNSWB+
U410
3.3V
2 3
VIN VOUT
R460
5
4
R419
3
LI_ION
1
BOOT_CTRL
2
TP405
TEST_POINT
C434