Hytera MD652, Service Manual

Page: 124 / 207

Circuit Description
VHF1 (136
‐
174 MHz)
16
Emergency Alarm
When the emergency alarm pin is at low level, R2048 is grounded, and Q2010 is turned on to supply
power for the whole system. Meanwhile, Q2011 is also turned on. When low level is detected from
U1002 but the radio is powered off, the system will output the level Pwr_Hold and send emergency
alarm signal. If the radio is powered on then, the system will directly output emergency alarm signal.
Power-up Process
Step 1 Power on the radio using one of the three methods (Power On/Off key, Ignition Signal, or
Emergency Alarm).
Step 2 U2012 generates reset signal and remain a low level for 1.25 seconds, allowing the processor
to get started.
Step 3 Power-on signal will be sent to the processor.
Step 4 After receiving the signal, the processor generates the level of Pwr_Hold. Then the power-up
processes are completed.
Clock
Input Clock
The 32K clock provided by X1001 is mainly used for timing and sleeping of the system. The frequency of
the 32K clock is 32.768 kHz, which is divided by U1002 by 32768 times in all to 1Hz for counting
seconds. The system clock (19.2 MHz) is generated by an external crystal oscillator.
Output Clock
The baseband outputs 3 clock signals to send to U3001, U8001 and Option Board respectively.