Kenwood NXR-700 Service Manual page 22

NXR-700
■ TX_Vocoder DSP
In NXDN mode, the AMBE+2 (TM) vocoder processing is
performed by the IC324 TX_Vocoder_DSP.
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 limitation filter (root nyquist
cosine fi lter and sinc fi lter). The passed signal turns into a
modulating 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
NXR-700 rapidly shift to the power down state. The IC325
A/D converter (pin 124) monitors the voltage. It detects the
voltage rises and returns to the normal voltage range.
■ Reset circuit
Reset system diagrams of each device of NXR-700 are
attached. With regard to the priority of the reset signal of
each device, IC303 that prepares the reset signal of IC325
has the highest priority. Software of IC325 can activate de-
vices including IC323, IC324, IC703, IC700, IC702, IC719,
IC34, and IC17. Software of IC703 can activate the reset of
IC325.
33MPU
33MPU 33MPU
IC303
33MPU
22
CIRCUIT DESCRIPTION
D16C_RST
33SH 33SH
33SH
IC708
SYS_RST
33MPU
IC325
IC314
RESET_D
33MPU 33MPU
IC324
DSP_RST
Fig. 26 Reset circuit
■ Clock shift circuit
NXR-700 control unit has a crystal oscillation circuit
shown below.
X53-4132-71:
X53-4140-10:
Each oscillation circuit turns on the NPN transistor
"2SC4738(GR)F" and staggers the oscillating frequency
by approximately –70ppm. This may prevent interference
against transmitter and receiver frequencies. Each transistor
is turned on and off by the FPU.
■ Flash memory (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 128M bit memo-
ry used by the Main MPU.
33SH 33BU
IC703 IC700
50MPU
from RTE
33SH
IC323 IC17
14.7456MHz (IC34 and X1)
16.515072MHz (IC37 and X2)
14.7456MHz (IC325 and X301)
25.8048MHz (IC37 and X2)
25MHz (IC719 and X702)
33SH 33SH 33SH
IC719 IC702
50MPU 33SH
IC34
50MPU 50MPU
WP
IC35
50MPU 50MPU 33SH
WP
EEPROM
each IC37
RF unit