Kenwood NX-300 Service Manual page 17

6-2. Memory Circuit
The memory circuit consists of the ASIC (IC108) and the
SRAM(IC103) and flash memory (IC101). The flash 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 capacity of 1M-bit that
contains work area and data area.
Flash memory
■
Note: The flash memory stores the data that is written by the
FPU (KPG-111D/111DN), tuning data (Deviation, Squelch,
etc.) ,and firmware program (User mode, Test mode, Tuning
mode, etc.). This data must be rewritten when replacing the
flash memory.
SRAM (Static memory)
■
Note: The SRAM has temporary data area and work area.
When the power supply is off, it is backed up by an internal
secondary lithium battery. Therefore, the saved data is not
lost.
Real-time clock
■
The clock function is based on real-time clock IC (IC106).
When the power supply is off, it is backed up by an internal
secondary lithium battery.
6-3. LCD
The LCD is controlled using the bus lines on the connec-
tor (CN1) of the Control unit (XC1-002). It corrects the LCD
contrast voltage using IC1.
6-4. Key Detection Circuit
Keys are detected using the key scan circuit in IC108.
The /KEYI* signals that are normally pulled down go high
when any key is pressed.
6-5. Low Battery Warning
The battery voltage is divided using R444 and R445 and
is detected by the ASIC (IC108). When the battery voltage
falls below the voltage set by the Low battery warning ad-
justment, 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 switch is pressed.
CIRCUIT DESCRIPTION
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.
6-6. DSP
The DSP circuit consists of a DSP (IC719) and process-
es the base band signal. The DSP operates on an external
clock of 18.432MHz (the same as the IC108), the I/O section
operates at 3.3V and the core section operates at 1.5V. The
DSP carries out the following processes:
• 4 Level FSK processing
• Analog FM pre-emphasis/de-emphasis
• Vocoder processing between audio codec and modula-
tion/demodulation
• CAI processing, such as error correction encoding
• QT/DQT encoding/decoding
• LTR encoding/decoding
• DTMF encoding/decoding
• MSK encoding/decoding
• 2-tone encoding/decoding
• Compressor/expander processing
• Voice scrambler processing
• Transmit/receive audio filtering processing
• Microphone amplifier AGC processing
• Audio mute processing
• Modulation level processing
7. Power Supply Circuit
The battery voltage (+B) is provided from the battery
terminal on the TX-RX unit (XC1-013). The battery voltage
passes through the 2.5A fuse (F900), and goes to the RF
final amplifier, AVR ICs (IC902, IC903), and Control unit
(XC1-002).
In the control unit, +B is connected to the DC/DC (IC407),
AVR ICs (IC411, IC708, IC416), and voltage detector IC
(IC414). The voltage detector watches the battery voltage.
If the battery voltage is 5.6V or higher, the detector outputs
High. While the output of IC414 is High, IC416 and Q409
provide 3.1V (31BU) to the backup-section.
When the VOL SW is turned on, SB1 becomes high (bat-
tery voltage). The DC/DC (IC407) operates if both SB1 and
the output of the detector are high. IC407 outputs 3.8V and it
activates IC404 (33M), IC717 (15M), and IC406 (33A). As a
result, the ASIC and DSP operate.
The SBC signal becomes High after the ASIC operates,
IC708 (5A), Q403 on the Control unit (SB2) and Q901 on the
TX-RX unit (SB3) are turned on. IC901 and IC903 operate
by turning on these AVR ICs and FET switches.
The 5UC signal becomes High when an option is in-
stalled on the universal connector. Then IC411 (50U) oper-
ates.
When the /SAVE signal becomes High, IC902 (50C)
operates. The output of IC902 is connected to three FET
switches (Q902, Q903, Q905). When the SBC signal be-
comes High, IC903 (33C) operates. The FET switches are
controlled by the CPU. Q905 (50T) is turned on in transmit
mode. Q902 (50R) and Q903 (50IF) are turned on in receive
mode.
When the VOL SW is turned off the /PSW signal be-
comes Low. After detecting the /PSW signal, the ASIC
changes SBC signal to Low. Then the power supplies except
IC416 (31BU) stop.
NX-300(G)
17