Control Circuit; Pll; Memory Circuit; Low Battery Warning - Kenwood NX-1200 Series Service Manual

2.3.5.3

PLL

PLL (IC2) compares the difference in phases of the VCO oscillation signal and the TCXO (X1) reference frequency. And it returns the
difference voltage to the VCO CP terminal and realizes the "Phase Locked Loop". This allows the VCO oscillation frequency to
accurately match (lock) the desired frequency.
When the frequency is controlled by the PLL, the frequency convergence time increases as the frequency difference increases when
the set frequency is changed. To supplement this, The ASSIST Voltage from D/A converter (IC604) is used before control by the PLL
(IC2) to bring the VCO oscillation frequency close to the desired frequency. As a result, the VCO CP voltage does not change and is
always stable at approx. 2.5V.
The desired frequency is set for the PLL (IC2) by the MPU/DSP (IC501) through the 3-line "PLL_LE", "PLL_DATA", "PLL_CLK" serial
bus for PLL. IC501 monitors through the "PLL_LD", whether the PLL (IC2) is locked or not. If the VCO does not lock to desired
frequency (unlock), the "PLL_LD" logic is low.

2.3.6 Control Circuit

The control circuit consists of MPU/DSP (IC501) and its peripheral circuits. IC501 mainly performs the following;
(1) Switching between transmission and reception by PTT signal input.
(2) Reading system, zone, frequency, and program data from the memory circuit.
(3) Sending frequency program data to the PLL.
(4) Controlling the audio mute circuit by decode data input.
2.3.6.1 MPU/DSP
This MPU/DSP (IC501) operates at 168MHz (MAX) clock and 3.2V DC. Controls the flash memory, the receive circuit, the transmitter
circuit, the control circuit, and the display circuit.
2.3.6.2

Memory Circuit

Memory circuit consists of the MPU/DSP (IC501) and the flash memory (IC500). The flash memory has capacity of 16Mbit that
contains the transceiver control program for the MPU/DSP and stores the data. It also stores the data for transceiver channels and
operating parameter that are written by the FPU. This program can be easily written from external devices.
Flash memory
Note:
The flash memory (IC500) stores the data that is written by the FPU (KPG-D6/D6N), tuning data (Deviation, Squelch, etc.), and other
data (User mode, Test mode, Tuning mode, ESN, etc). If changing the flash memory, please contact our service center.
2.3.6.3

Low Battery Warning

The battery voltage is divided using R110 and R111, it is detected by A/D converter (incorporated in MPU/DSP (IC501)). When the
battery voltage falls below the voltage set by the Low battery warning adjustment, the red LED blinks to notify the operator that it is
time to replace the battery. If the battery voltage falls even more (approx. 5.8V), a beep sounds and transmission stops.
Low battery warning
The red LED blinks during transmission.
The red LED blinks and the warning tone beeps while the
PTT is pressed.
2.3.6.4 DSP
The DSP circuit consists of a MPU/DSP (IC501) and processes the base band signal. The MPU/DSP operates at 168MHz (MAX)
clock, the I/O section operates at 3.2V.
The DSP carries out the following processes:
• 4-Level FSK processing
• Analog FM pre-emphasis/de-emphasis
• Vocoder processing between audio and modulation/demodulation
• CAI processing, such as error correction encoding
• QT/DQT encoding/decoding
• DTMF encoding/decoding
• MSK encoding/decoding
• 2-tone encoding/decoding
• Compressor/expander processing
• Voice scrambler processing
• Transmit/receive audio filtering processing
• Audio mute processing
• Modulation level processing
• Active Noise Reduction
• Voice announce processing
1-10 (No.RA077<Rev.001>)
Battery condition
The battery voltage is low but the transceiver is still usable.
The battery voltage is low and the transceiver is not usable to make calls.