Kenwood NX-411 Service Manual page 17

6. Control Circuit
The control circuit consists of the ASIC (IC309) and its
peripheral circuits. IC309 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 by decode data input.
6-1. ASIC
The ASIC (IC309) is a 32-bit RISC processor, equipped
with peripheral function and ADC/DAC.
This ASIC operates at 18.432MHz clock and 3.3V/1.5V
DC. It controls the fl ash memory, SRAM, DSP, receiver cir-
cuit, transmitter circuit, control circuit, and display circuit and
transfers data to or from an external device.
6-2. Memory Circuit
The memory circuit consists of the ASIC (IC309), the
SRAM (IC305), and the fl ash memory (IC303).
The fl ash memory has a 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 op-
erating parameters 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 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 has a 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 a real-time clock IC (IC308).
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 con-
nector (CN301) of the Display unit (X54-377). It corrects the
LCD contrast voltage using IC102.
6-4. Temperature Detection Circuit
The temperature detection circuit detects the temperature
using a temperature IC (IC502) and corrects the thermal
characteristic change of the squelch or LCD.
CIRCUIT DESCRIPTION
6-5. Key Detection Circuit
/KEYI
any key is pressed.
6-6. Low Battery Warning
is detected by the ASIC (IC309). 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.
The red LED blinks during
transmission.
The red LED blinks and the
warning tone beeps while the
PTT switch is pressed.
6-7. DSP
es the baseband signal. The DSP operates on an external
clock of 18.432MHz (the same as IC309), the I/O section
operates at 3.3V and the core section operates at 1.5V. The
DSP carries out the following processes:
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7. Power Supply Circuit
minal on the TX-RX unit (X57). The battery voltage passes
through the 2.5A fuse (F201), and goes to the RF fi nal am-
plifi er, AVR ICs (IC204, IC205, IC210, IC18), DC/DC (IC206)
and voltage detector IC (IC209).
battery voltage is 5.6V or higher, the detector outputs High.
While the output of IC209 is High, IC210 and Q208 provide
3.1V (31BU) to the backup-section.
tery voltage). The DC/DC (IC206) operates if both SB1 and
the output of the detector are high. IC206 outputs 3.8V and
activates IC203 (33M), IC202 (15M), and IC201 (33A). As a
result, the ASIC and DSP operate.
Keys are detected using a key scan circuit in IC309. The
* signals that are normally pulled down go high when
The battery voltage is divided using R224 and R225 and
Low battery warning
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.
The DSP circuit consists of a DSP (IC304) and process-
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
Compressor/expander processing
Voice scrambler processing
Transmit/receive audio fi ltering processing
Microphone amplifi er AGC processing
Audio mute processing
Modulation level processing
The battery voltage (+B) is provided from the battery ter-
The voltage detector watches the battery voltage. If the
When the VOL SW is turned on, SB1 becomes high (bat-
NX-411
Battery condition
17