Control Circuit; Cpu; Power Supply Circuit; Key Detection Circuit - Kenwood NX-800 Service Manual

NX-800

6. Control Circuit

The control circuit consists of CPU (IC510) and its periph-
eral 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 by decode data input.

6-1. CPU

The CPU (IC510) is 32bit RISC processor, equipped with
peripheral function and ADC/DAC.
This CPU operates at 18.432MHz clock and 3.3V /1.5V DC.
Controls the flash memory, SRAM, DSP, the receive circuit,
the transmitter circuit, the control circuit, and the display
circuit and transfers data to or from an external device.
6-2. Memory Circuit
Memory circuit consists of the CPU (IC510) and the SRAM
(IC503), the flash memory (IC501). The flash memory has
capacity of 32Mbit that contains the transceiver control
program for the CPU 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 1Mbit that
contains work area and data area.
■ Flash memory
Note: The flash memory stores the data that is written by the
FPU (KPG-111D), tuning data (Deviation, Squelch, etc.), and
firmware program.
■ 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 save data does not
break.
■ Real-time clock
The clock function is based on 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 CPU (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.
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CIRCUIT DESCRIPTION

6-4. Key Detection Circuit

and KO* signals that are normally pulled up go low when any
key is pressed.
6-5. DSP
the base band signal. The DSP operates on an external clock
of 18.432MHz (the same as the IC510), the I/O section oper-
ates at 3.3V and the core section operates at 1.5V. The DSP
carries out the following processes:

7. Power Supply Circuit

(IC405). IC405 regulates +B voltage to 5.0V (50M). 50M
operates whenever +B is supplied. IC402 (33M), IC408 (33A)
and IC409 (15M) are enabled while the 50M are operating.
memory. At this time CPU starts working. Voltage detector
IC (IC401) watches +B voltage. If +B voltage is higher than
8.6V, IC401 (/BINT) outputs High. If the /BINT signal is high,
Q404 (SB SW) is turned on by SBC signal from CPU. (High :
SB=ON, Low : SB=OFF). When the SB is turned on, IC403
(80C), IC404 (50C), IC406 (33C), IC407 (33GPS) and IC410
(150C) start working. Q416 and Q412 are controlled by SBC
signal. If the SBC signal becomes High, Q416 (33A-2) oper-
ates and Q412 (50MC SW) are turned on.
sion to supply power (80T) for transmission circuit. The CPU
controls the signals (RXC) to High during reception to supply
power (80R, 50R) for reception circuit.
IGN (Ignition sense) signal or /BINT signal, it controls the SBC
signal to Low, and turns the transceiver power (SB) off.
When D401 and Q401 detect over-voltage condition, they
turns Q404 (SB SW) off. But the CPU still works.
provided to SRAM and RTC through the secondary battery
connected with CN405.
Keys are detected using Key scan circuit in IC911. The /KI*
The DSP circuit consists of a DSP (IC502) and processes
• 4Level 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
• DTMF encoding/decoding
• MSK encoding/decoding
• 2TONE encoding/decoding
• Compressor/expander processing
• Voice scrambler processing
• Transmit/receive audio filtering processing
• Microphone amplifier AGC processing
• Audio mute processing
• Modulation level processing
+B is connected to Final amplifier and DC/DC converter IC
33M and 15M provide the power to CPU, DSP, and Flash
The CPU controls the TXC signal to High during transmis-
When the CPU detects the PSW (Power switch) signal,
If +B is not provided to the transceiver, the power is