Kenwood NXR-901 Service Manual page 21

■ TX_Vocoder DSP
In digital mode, vocoder processing is performed by the
IC324 TX_Vocoder_DSP.
The audio signal input from the Audio codec IC ADC part
(IC309 AINL) terminal is vocoder encode processed and
converted to audio data.
CAI data is encoded for correcting errors and converted
to transmitter data.
This data is framed, converted to symbol values and
made to pass the baseband limit fi lter (root nyquist cosine
fi lter and sinc fi lter).
The passed signal turns into a MOD signal. It is output
as an analog signal by the Audio codec IC DAC part (IC309
AOUTR terminal).
■ Power supply voltage monitoring circuit
This circuit always monitors the external power supply
voltage assuming that the abnormal power supply voltage is
applied.
This circuit consists of X53-413 R67, R68, R71, and R79
and IC7, and X53-414 IC308. If the voltage is reduced, these
circuits interrupt the Modem control MPU (IC325) and the
NXR-901 rapidly shifts to the power down state.
The IC325 A/D converter (pin 124) monitors the voltage.
It detects voltage rises and returns it to the normal voltage
range.
■ Reset circuit
Reset system diagrams of each device of the NXR-901
are attached. With regards to the priority of the reset sig-
nal of each device, IC303 that prepares the reset signal of
IC325 has the highest priority.
The IC325 software can activate devices including IC323,
IC324, IC703, IC700, IC702, IC719, IC34, and IC17. The
IC703 software can activate the reset of IC325.
33MPU
33MPU 33MPU
IC303
RESET_D
33MPU
CIRCUIT DESCRIPTION
33SH
D16C_RST
33SH 33SH
IC703
33SH
IC708
SYS_RST
33MPU
IC325
IC314
33MPU 33MPU
IC324 IC323
DSP_RST
Fig. 23 Reset circuit
■ Clock shift circuit
The NXR-901 Control unit has a crystal oscillation circuit
as shown below.
X53-4132-71:
14.7456MHz (IC34 and X1)
16.515072MHz (IC37 and X2)
X53-4140-10:
14.7456MHz (IC325 and X301)
25.8048MHz (IC37 and X2)
25MHz (IC719 and X702)
Each oscillation circuit turns on the NPN transistor
"2SC4738 F" and staggers the oscillating frequency by ap-
proximately -70ppm.
This may prevent interference against transmitter and re-
ceiver frequencies.
Each transistor is turned on and off by the FPU.
■ Flash memory (for Main MPU)
IC702 is a 128M-bit Flash memory and contains the fi rm-
ware of the Main MPU.
■ Flash memory (Modem control MPU)
IC314 is an 8M-bit Flash memory and contains the fi rm-
ware of the Modem control MPU, RX DSP, and TX_Vocoder_
DSP.
■ SDRAM
IC704 and IC707 are program execution memory used
by the Main MPU, and use two 128M-bit.
■ SRAM
IC700 is a memory backed up by a lithium battery
(BA300).
The capacity is 16M-bit. It contains data required for the
system backup.
33BU
33SH
IC700
50MPU
from RTE
50MPU
WP
33SH
50MPU
WP
IC17
NXR-901
33SH 33SH
IC719 IC702
50MPU 33SH
IC34
50MPU
IC35
50MPU 33SH
EEPROM
each IC37
RF unit
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