Kenwood NX-900 Service Manual page 21

6. Control Circuit
The control circuit consists of the ASIC (IC510) and its
peripheral circuits. IC510 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 squelch on/off by the DC voltage from the
squelch circuit.
5) Controlling the audio mute circuit through decode data
input.
6-1. ASIC
The ASIC (IC510) is a 32-bit RISC processor, equipped
with peripheral function and ADC/DAC.
This ASIC operates at a 18.432MHz clock and 3.3V /1.5V
DC. It controls the fl ash memory, SRAM, DSP, receive cir-
cuit, transmit circuit, control circuit, and display circuit and
transfers data to or from an external device.
6-2. Memory Circuit
Memory circuit consists of the ASIC (IC510) and SRAM
(IC503), and the fl ash memory (IC501). The fl ash memory
has capacity of 32M-bit that contains the transceiver control
program for the ASIC 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. The SRAM has a capacity of 1M-bit
that contains the work area and data area.
■ Flash memory
Note: The fl ash memory stores the data that is written
by the FPU (KPG-111D), tuning data (Deviation, Squelch,
etc.), and fi rmware program (User mode, Test mode, Tuning
mode, etc.). This data must be rewritten when replacing the
fl ash memory.
■ SRAM (Static memory)
Note: The SRAM a has temporary data area and work
area.
When the power supply is off, it is backed up by an inter-
nal secondary lithium battery. Therefore, the save data does
not break.
■ Real-time clock
The clock function is based on a real-time clock IC (IC504).
When the power supply is off, it is backed up by an internal
secondary lithium battery.
6-3. Display Unit
The display unit is composed of the MCU (IC911) and
the memory IC (IC913), and the LCD & Key backlight, etc.
The LCD Ass'y (with LCD Driver) is controlled using the
bus lines on the connector (CN905) of the display unit. It
corrects the LCD contrast voltage using IC909.
CIRCUIT DESCRIPTION
6-4. Key Detection Circuit
The /KI* and KO* signals that are normally pulled up go low
when a key is pressed.
6-5. DSP
the baseband signal. The DSP operates on an external clock
of 18.432MHz (the same as IC510), the I/O section operates
at 3.3V and the core section operates at 1.5V. The DSP car-
ries out the following processes:
• 4 Level FSK processing
• Analog FM pre-emphasis/de-emphasis
• Vocoder processing between audio codec and modula-
• CAI processing, such as error correction encoding
• QT/DQT encoding/decoding
• LTR encoding/decoding
• DTMF encoding/decoding
• MSK encoding/decoding
• Compressor/expander processing
• Voice scrambler processing
• Transmit/receive audio fi ltering processing
• Microphone amplifi er AGC processing
• Audio mute processing
• Modulation level processing
7. Power Supply Circuit
converter IC (IC405). IC405 regulates the +B voltage to
5.0V (50M). 50M operates whenever +B is supplied. IC402
(33M), IC408 (33A) and IC409 (15M) are enabled while 50M
is operating. Q412 is controlled by the SBC_2 signal. If the
SBC_2 signal becomes High, it operates and Q416 (33A2
SW) is turned on. Q412 is controlled by the SBC_2 or 33M
signal via D408. If the SBC_2 or 33M signal becomes High,
it operates and Q412 (50MC SW) is turned on.
and Flash memory. At this time the ASIC starts working.
The voltage detector IC (IC401) watches the +B voltage. If
the +B voltage is higher than 8.6V, IC401 (/BINT) outputs
High. If the /BINT signal is high, Q404 (SB SW) is turned on
by the SBC_2 signal from the ASIC. (High : SB=ON, Low
: SB=OFF). When the SB is turned on, IC403 (80C), IC404
(50C), IC406 (33C) and IC407 (33GPS) start working.
sion to supply power (80T) to the transmission circuit. The
ASIC sets the RXC signal to High during reception to supply
power (80R, 50R) to the reception circuit.
IGN (Ignition sense) signal or /BINT signal, it sets the SBC
signal to Low, and turns the transceiver power (SB) off.
When D401 and Q401 detect an over-voltage condition,
they turns Q404 (SB SW) off, but the ASIC continues to
work.
Keys are detected using the Key scan circuit in IC911.
The DSP circuit consists of a DSP (IC717) and processes
tion/demodulation
+B is connected to the Final amplifier and the DC/DC
33M and 15M provide the power to the ASIC, DSP,
The ASIC sets the TXC signal to High during transmis-
When the ASIC detects the PSW (Power switch) signal,
NX-900
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