Kenwood NXR-700 Service Manual page 23

■ SRAM
IC700 is a memory backed up by a lithium battery
(BA300).
The memory size is 16M bits. It contains data required
for the system backup.
■ Frame synchronizing signal transmitter and
receiver circuit
J702 and J703 are connectors for synchronizing with
other repeaters in NXDN trunking mode. The differential
rectangular wave that conforms to RS-485, 12.5Hz or 25Hz
is input to and output from this connector for synchronizing
multiple repeaters.
In the repeater system, any given repeater outputs a
synchronizing signal and that synchronous signal is input to
other remaining repeaters.
With regards to the output of the synchronous signal, the
frame signal generated by TX_Vocoder_DSP (IC324) is dif-
ferentially output by IC302.
With regards to the input of the synchronous signal,
IC302 receives a differential signal, and is input to the in-
terruption of the RX DSP (IC323) and TX_Vocoder_DSP
(IC324).
■ 12.288MHz clock circuit
The clock circuit is installed in the control unit (X53-414)
for operating the RX DSP and TX_Vocoder DSP.
The clock circuit consists of X300 (12.288MHz TCXO),
Q304, and IC313.
12.288MHz from X300 is amplifi ed by Q304, IC313 and
becomes a clock for the RX DSP and TX_Vocoder DSP.
SR_CLK SR_CLK
SR_DATA SR_DATA
SR_OE SR_OE
SR_ SQ DATA
DATA
Shift register Shift register
IC925 IC924
SW SW SW SW
STATUS LED CTRL POWER TX BUSY OCXO
1~8
CIRCUIT DESCRIPTION
PF KEY1~6
SR_CLK
SR_DATA
SR_OE
SQ DATA SQ
Shift register
IC923
SW SW SW
KEY LED
1~6
Fig. 27 Shift register circuit (Display part)
7. Display Circuit
7-1. Display circuit
The display circuit (X56-311 B/3,C/3) consists of various
types of LEDs, 17-segment type D960, D961 (red), D921
(red: transmission), two-color type D920 (green: busy),
D922 (green: power on, red blinking: abnormal voltage),
D923 (green: CTRL), two-color type D924 (red: OCXO error,
green: OCXO normality, orange: external reference signal),
8-bit status LEDs D925 to D932, and LEDs with built in
switches S920 to S925.
IC920 to IC925 and IC960 to IC963 are in charge of dis-
playing present channels and states on the front panel.
IC923 to IC925 and IC960 to IC963 are shift registers that
convert the MPU serial data to parallel data and turn on
LEDs.
7-2. Key switches circuit
The logic signals from the front panel key and channel
switches (channel selector) are entered directly into the RF
MPU (IC34).
SR_CLK SR_CLK
SR_DATA SR_DATA
SR_OE SR_OE
DATA SQ DATA SQ
Shift register Shift register
IC963 IC962
SW SW SW
D961
NXR-700
SR_CLK SR_CLK
SR_DATA SR_DATA
SR_OE SR_OE
DATA SQ DATA SQ
Shift register Shift register
IC961 IC960
SW SW SW
D960
23