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NXR-901
■ Modem control MPU
The modem control MPU (IC325) is 16-bit single chip
microprocessor incorporating 256K bytes of ROM and 20K
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 digital mode, the IF signal input from the ADC (IC312)
to the RX DSP is limited to a very narrow band. So, it passes
through the IF band limitation band.
X702
25MHz
(Compact
LAN IC
Flash)
IC719
Flash memory
IC702
SDRAM
IC704,707
SRAM
IC700
Backup
BA300
FRAME
Flash memory
IC302
IC314
RX DSP
IC323
TX_Vocoder
DSP
IC324
VCXO
Buffer
12.288MHz
IC313
X300
PLL IC
19.2MHz
IC315
20
CIRCUIT DESCRIPTION
Q704,Q705
Beat
SW
shift
EEPROM
RS-232C
IC705
IC720
X700
25.8048MHz
Q700
Main
Q702
MPU
SW
IC703
Beat shift
RTC IC
IC701
X701
UART
32.768kHz
X301
14.7456MHz
Modem
Q307
control
Q308
SW
MPU
IC325
Beat shift
CODEC IC
IC309
OCXO control
Fig. 22 Control circuit
This signal is demodulated by the wave detection pro-
cessing par t. 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 digital data. Its frame timing is detected
and decoded for CAI data error correction.
Sound 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
UART
X1
14.7456MHz
RF
control
MPU
Q4
IC34
Q5
SW
Beat shift
SR_CLK
SR_DATA
STB
Shift register IC
TEST/SPKR
STB1
Shift register circuit (Display part)
STB_1
Shift register
Flash memory
IC17
X2
Q10,Q12
16.515072MHz
Beat
SW
shift
DSP
Divider
IC37
IC31
CODEC IC
IC4
QS
DATA
Shift register IC
IC22
IC1
Option
AOUT1~5
board
Refer to Fig. 24.
(TX unit)
STB
SR_CLK
SR_DATA
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