Kenwood NXR-700 Service Manual page 21

■ Modem control MPU
Modem control MPU (IC325) is 16-bit single chip micro-
processor incorporating 256 kilobytes of ROM and 20 kilo-
bytes of RAM.
This MPU controls the Flash memory, two DSPs, the
OCXO unit in the transmitter unit (X42-328) and the PLL cir-
cuit.
It also monitors the external power supply voltage. If the
voltage is abnormal, it stops the system.
■ RX DSP (IC323)
In NXDN mode, the IF signal input from the ADC (IC312)
to the RX DSP is limited to a narrow band or a very narrow
X702
Q704,Q705
25MHz
LAN IC
(Compact
Flash) IC719
Flash memory
IC702
SDRAM
IC704,707
SRAM
IC700
Backup
BA300
FRAME Flash memory
IC302 IC314
RX DSP
IC323
TX_Vocoder
DSP
IC324
TCXO
Buffer
12.288MHz
IC313
X300
CIRCUIT DESCRIPTION
Beat
SW
shift
EEPROM RS-232C
IC720 IC705
UART
X700
25.8048MHz
Q700
14.7456MHz
Main
Q702
MPU
SW
IC703
Q4
Q5
Beat shift
RTC IC
Beat shift
IC701
X701
UART
32.768kHz
X301
14.7456MHz
Modem
Q307
control
Q308
MPU
SW
IC325
Beat shift
CODEC IC
IC309
OCXO control
Fig. 25 Control circuit
band. So, it passes through the IF band limitation band.
This signal is demodulated by the wave detection pro-
cessing part. The demodulated wave is made to pass
through the baseband limitation filter (root nyquist cosine
fi lter and 1/sinc fi lter).
This signal is symbol-detected and bit-judged, and is
then converted to NXDN data. Its frame timing is detected
and decoded for CAI (Common Air Interface: NXDN format)
data error correction.
Audio data is vocoder decode processed by the IC324
TX_Vocoder_DSP. It is then converted into the PCM signal.
It is analog-output as an audio signal by the DAC part of the
Audio codec IC (IC309 AOUTL terminal).
Dsub25
CN58
Flash memory
16.515072MHz
X1
RF
control
MPU
IC34
SW
CODEC IC
SR_CLK
SR_DATA
QS
STB
Shift register IC
IC22
TEST/SPKR
AOUT1~5
STB1
Shift register circuit (Display part)
STB_1
Shift register
(TX unit)
NXR-700
IC17
X2
Q10,Q12
Beat
SW
shift
DSP Divider
IC37 IC31
IC4
DATA
Shift register IC
IC1
Option
board
Refer to Fig. 27.
STB
SR_CLK
SR_DATA
21