Control Circuit; Frequency Shift Circuit; Memory Circuit; Low Battery Warning - Kenwood NX-340 Service Manual

2.1.5 Control Circuit

The control consists of the MCU (IC710) and its peripheral circuits. It controls the TX-RX unit. IC710 mainly performs the following;
(1) Switching between transmission and reception via the PTT signal input.
(2) Reading channel information, frequency, and program data from the memory circuit.
(3) Sending frequency program data to the PLL.
(4) Controlling squelch on/off via the DC voltage from the squelch circuit.
(5) Controlling the audio mute circuit via the decode data input.
(6) Transmitting tone and encode data.
2.1.5.1

Frequency Shift Circuit

The MCU (IC710) and baseband IC (IC705) operate at a clock frequency of 19.2MHz.
This oscillator frequency can be shifted by pin 8 of the MCU (IC710). When pin 8 is set to high, the beat shift function is ON.
A beat sound may be able to be evaded from generation if "Beat Shift" is set to ON when it is generated in the internal spurious trans-
mission modulated sound of the transceiver.
2.1.5.2

Memory Circuit

The Memory circuit consists of the MCU (IC710) and EEPROM (IC700). The EEPROM has a capacity of 64K-bit and stores the chan-
nel information, the last channel data, the scan on status, and other parameters.
EEPROM
Note:
The EEPROM stores tuning data (Deviation, Squelch, etc.).
Realign the transceiver after replacing the EEPROM.
2.1.5.3

Low Battery Warning

The battery voltage is monitored by the MCU (IC710 pin 33: BATT). When the battery voltage falls below 6.4V approximately, the red
LED blinks, notifying the operator that it is time to replace the battery (When "Always" option (default setting) under the Battery Warning
function in the FPU is selected).
If the battery voltage falls below 5.8V approximately, the transceiver does not transmit and a warning tone beeps when the PTT switch
is pressed (When the Battery Warning Tone is selected in the FPU).
2.1.5.4 Key Input
Keys and channel selector circuit.
The signal from the keys and channel selector are directly input to the MCU, as shown in Figure 8.
IC710
MCU
BSHIFT XIN
8 12
19.2MHz
H: OFF
1
X2
L: ON
TCXO
3
Fig.7 Frequency shift circuit
Selector
IC710
MCU
66
EN4 PTT
64
EN3
Side1
65
EN2
63
EN1 Side2
Fig.8 Key input
IC705
Baseband IC
XTAL
39
6
IC713
CLK AMP
2
4
PTT
SW
Side1
59
60
Side2
61
(No.RA003<Rev.004>)1-7