NX-320
16
6-3. LCD
The LCD is controlled using the 4 serial lines (SDI0, /
LCDCS, SCK0, SDO0) from the ASIC (IC610).
6-4. Key detection circuit
Keys are detected using the LCD controller driver IC (IC8).
If a pressed key is detected by IC8, it is informed to IC610
through the serial line.
6-5. Low battery warning
The battery voltage is divided using R514 and R515 and
is detected by the ASIC (IC610). 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
Battery condition
The red LED blinks during
transmission.
The battery voltage is low but
the transceiver is still usable.
The red LED blinks and the
warning tone beeps while the
PTT switch is pressed.
The battery voltage is low and
the transceiver is not usable to
make calls.
6-6. DSP
The DSP circuit consists of a DSP (IC603) and processes
the baseband signal. The DSP operates on an external clock
of 18.432MHz (the same as the IC610), the I/O section op-
erates 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
• 5-tone 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
The battery voltage (+B) is provided from the battery
terminal on the TX-RX unit (X57). The battery voltage passes
through the 2.5A fuse (F1), and goes to the RF fi nal ampli-
fi er, AVR ICs (IC504, IC902), DC/DC converter (IC506), and
voltage detector IC (IC507). The voltage detector watches
the battery voltage. If the battery voltage is 5.6V or higher,
the detector outputs High.
When the VOL SW is turned on, SB1 becomes high (bat-
tery voltage). DC/DC (IC506) operates if both SB1 and the
output of the detector are high. IC506 outputs 3.8V and
activates IC502 (33M), IC503 (15M), IC501 (33A) and IC505
(33C). As a result, the ASIC and DSP operate.
The SBC signal becomes High after the ASIC operates,
IC504 (50C), IC902 (50V) and Q501 (SB2) are turned on.
When the /SAVE signal becomes High, Q512 (50C) oper-
ates. Switches (Q503, Q505) are controlled by the ASIC.
Q505 (50T) is turned on in transmit mode. Q503 (50R) is
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 the SBC signal to Low.
50C is fed to IC509 (100C). IC509, D511 and D512 con-
sist of a voltage doubler. C543 is charged to 5V by 50C and
switched to C545 by the “DDCLK” control signal. The 100C
circuit then outputs approxi10VDC.
8. Signaling Circuit
8-1. Encode (QT/DQT/LTR/DTMF/2-tone/5-tone/MSK)
Each signaling data signal of QT, DQT, LTR, DTMF,
2-tone/5-tone and MSK is generated by the DSP circuit, su-
perimposed on a modulation signal and output from IC610.
Each deviation of the TX QT, DQT, LTR, DTMF, 2-tone/5-tone
and MSK tone is adjusted by changing the output level of
IC603 and the resulting signal is routed to the VCO and PLL.
8-2. Decode (QT/DQT/LTR/DTMF/2-tone/5-tone/MSK)
The audio signal is removed from the FM detection signal
sent to the DSP circuit and the resulting signal is decoded.
9. Compander Circuit
The term “compander” means compressor and expand-
er. The compander reduces noise by utilizing a compressor
and an expander. The transceiver contains a DSP (IC603) to
perform this operation. The transceiver compander can be
turned on or off using the FPU.
CIRCUIT DESCRIPTION
