Kenwood NXR-800 Service Manual page 20

NXR-800
On the other hand, the transmitting audio signal output
from IC3 is amplifi ed by IC9 (A/4), applied to pin 3 (AINL)
of CODEC IC4, and is then converted from analog to digital
at a sampling frequency of 16.128kHz. The digitized trans-
mitting audio signal is AGC-processed, pre-emphasized
and fi ltered, except for the 300Hz to 3kHz range, by DSP
IC37, and is then feed back to CODEC IC4, converted from
■ Shift register circuit
The MPU (IC34) transmits serial data to shift registers
IC923 from IC923 to IC960 and from IC960 to IC963 in the
display circuit (X56-312 B/3, C/3).
Additionally, it transmit serial data to the control unit (X53-
413) IC1 and IC22 and the transmitter unit (X56-312) IC703.
This serial data can control various functions of each unit.
■ Power supply circuit
This circuit consists of X53-413 IC6, IC10, IC11, IC15,
IC16 and 18, and X53-414 IC305, IC306, IC307 and IC329.
IC10 is a DC/DC converter that converts 13.8V to 5.0V.
IC11 is a DC/DC converter that converts 13.8V to 8.0V. IC16
is the 5.0V AVR and connected to IC10. IC6, IC15, IC305
and IC329 is the 3.3V AVR. IC18 is the 1.8V AVR. IC306 is
the 1.5V AVR. IC18 and IC306 is connected to IC329.
■ Flash ROM (RF control MPU)
IC17 is an 8M bit Flash ROM and contains MPU fi rmware
for controlling the RF.
■ EEPROMs circuit
The EEPROM is a built in receiver unit (X55-310), trans-
mitter unit (X56-312) and Final unit (X45-382).
The RF control MPU controls these EEPROMs by the IIC
bus.
20
CIRCUIT DESCRIPTION
RX detected signal
(AINR)
RD
TX modulation signal
Local Mic
(AINL)
TA
[Frequency response]
REPEAT
Fig. 24 An audio signal course and the frequency characteristic
digital to analog, and the analog signal is output from pin15
(AOUTL). The transmitting signal from the AOUTL is am-
plifi ed by IC9 (B/4), passed through the IC9 (C/4) low-pass
fi lter, and sent to the IC9 (D/4) summing amplifi er.
IC31 is a counter IC. The clock required for the CODEC
and DSP is generated by dividing the 16.515072MHz clock
signal supplied by the DSP IC37.
CODEC IC
IC4: AK4550VTP
2 16
RX
(AOUTR)
REPEAT
3
15
TX
(AOUTL)
TD
300Hz 3kHz
RX (De-emphasis)
TX (Pre-emphasis)
(300Hz~3kHz Flat)
6-2. X53-414
■ Main MPU
The Main MPU (IC703) is a 32-bit RISC microprocessor
incorporating a 16K bite cache memory.
The main MPU controls the Flash ROM, SDRAM, SRAM,
LAN IC, RS-232C driver, receiver and real-time clock (RTC)
IC besides RF control MPU and UART communication with
modem control MPU.
■ LAN interface
NXR-800 is equipped with a 100Base-TX or 10Base-T
LAN interface. This circuit consists of IC719, IC720 and
J700. IC719 is a control IC. IC720 is a EEPROM, and saves
the MAC address.
■ Real time clock (RTC) circuit
This circuit consists of IC710 and X701. IC710 is a Real
Time Clock. X701 is a crystal oscillator. IC710 is connected
to IC703 (Main_MPU) via the IIC bus. The oscillating fre-
quency of X701 is 32.768kHz. It is backed up by a recharge-
able lithium battery (BA300). The IC710 clock data is used
after resetting the backup.
■ RS-232C circuit
NXR-800 is equipped with a RS-232C interface. It is con-
nected to a PC with pin9 female RS-232C cross cable. It
uses the FPU and writes the fi rmware. IC705 is a RS-232C
driver receiver IC, and interfaces at the TTL232C level.
RA
RX audio amp.
TX VCO
(Modulation circuit)