Kenwood NEXEDGE NXR-710 Service Manual Download

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NXR-710

4-2. Memory circuit

The Memory circuit consists of the MCU (IC20), the

SRAM (IC9), and the fl ash memory (IC3).

The fl ash memory has a capacity of 32Mbit that contains

the transceiver control program for the MCU and stores the
data. It also stores the data for transceiver channels and
operating parameters that are written by the FPU. This pro-
gram can be easily written from external devices.

The SRAM has a capacity of 1Mbit that contains work

area and data area.

■

Flash memory

Note:

The fl ash memory stores the data that is written by

the FPU, tuning data (Deviation, Squelch, etc.), and firm-
ware program.

■

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.

4-3. DSP circuit

The DSP circuit consists of a DSP (IC6) and processes

the base band signal. The DSP operates on an external clock
of 18.432MHz (the same as IC20). The I/O section operates
at 3.3V and the core section operates at 1.6V. The DSP car-
ries out the following processes:

■

Digital processing

• 4Level FSK and Baseband fi lter processing
• Vocoder processing between audio codec and modula-

tion/demodulation

• CAI processing, such as error correction encoding/decod-

ing and interleaving

•  AFC loop control
•  Frame synchronization and Time tracking
•  Data scrambling

■

Analog FM processing

•  Pre-emphasis/De-emphasis
•  QT/DQT encoding/decoding
•  DTMF encoding/decoding
•  Compressor/Expander processing
•  Voice scrambler processing

■

Audio or Modulation function

•  Transmit/Receive audio fi ltering processing
•  Microphone amplifi er AGC processing
•  Audio soft mute processing
•  Modulation level processing
•  Squelch Filtering

■

Other function

•  Voting tone
•  CWID
•  Courtesy tone
•  Repeater operating
•  Analog/Digital Mixed mode

4-4. Squelch circuit

The Squelch circuit amplifi es the demodulated noise sig-

nal from IC6 after fi ltering through the BPF circuit. The pro-
cessed digital noise signal is applied to CODEC IC14, and is
converted from digital to analog. The amplifi ed signal is then
converted to a DC signal by the detection circuit. The con-
verted signal is fed back to IC20.

Squelch

DAC
IC14

/PDN,

LRCLK,

SDTI,

BICLK

Buffer

IC16

VCTCXO

(18.432MHz)

MAIN_CLK

XTAL_IN

ADC1

BSHIFT

/PCS_DSP

/SYMTIM, /DINT, /DWUP, FSDET, /HINT

MCSCKAF, /MCCSAF, MCDIAF, MCDOAF

/MCCSXCN, /MCCSRCN, MCDICN,

MCDOCN, MCSCKCN

A[0~17], D[0~7],

/RD, /WR, /CS2

A[0~21], D[0~15],

/RD, /WR, /CS0, /WP

A[0~20], D[0~15], /RD,

/WR, /HRDY, /CS3, /HDS2

VREF

AMP

IC13(A/2,B/2)

AMP

IC15(A/2)

AMP

LDR

/DRST

/FRST

/DRST

33M 16M

33BU

33M

33A

15M

FLASH

IC3

SRAM

IC9

DSP

IC6

MCU

IC20

Fig. 14 Control circuit

4-5. Power supply circuit

The X53-449 circuit consists of IC301, IC302, IC303,

IC304, IC305 and IC306.

IC301 is a DC/DC converter that converts 13.6V to 6.0V.

This 13.6V voltage is supplied from TX-RX unit (X57-794).

IC302 is connected to IC301 and regulates the voltage

to 5.0V. IC303, IC304, IC305 and IC306 are connected to
IC301. IC303 and IC306 are 3.3V voltage regulators. IC304
is a 1.5V regulator IC, and IC305 is a 1.6V regulator IC.

CN302 is the connector for the lithium battery. The

lithium battery is used to back up the SRAM and RTC data
when no external DC power source is available.

CIRCUIT DESCRIPTION