Memory Circuit; Low Battery Warning; Key Input; Signaling Circuit - Kenwood TK-D240 Service Manual

2.3.5.2

Memory Circuit

The Memory circuit consists of the MCU (IC710) and Flash memory (IC700). The Flash memory has a capacity of 4M-bit and stores
the channel information, the last channel data, the scan on status, and other parameters.
2.3.5.3

Low Battery Warning

The battery voltage is monitored by the MCU (IC710 pin 33: BATT). When the battery voltage falls below 7.0V 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).
2.3.5.4

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.

2.3.6 Signaling Circuit

2.3.6.1 Encode
 Low-speed data (QT, DQT)
Low-speed data is output from pin 29 of the MCU. The signal passes through the low pass CR filter, and goes to the audio processor
(IC705). The signal is mixed with the audio signal and goes to the VCO and TCXO (X1) modulation input after passing through the
D/A converter inside the audio processor (IC705) for BAL adjustment.
High-speed data (2-tone,DTMF)
High-speed data (HSD) is output from pin 30 of the MCU. HSD deviation made by an adjustment in the MCU is passed through the
low pass CR filter and is then mixed with the microphone signal before being applied to the baseband IC (IC705).
The output of the baseband IC, MOD1 and MOD2, will be fed into the TCXO and VCO respectively.
MSK (Fleet Sync/MDC-1200)
The MSK signal is generated in the audio processor (IC705). The signal passes through the D/A converter (inside the baseband IC:
IC705) and is routed to the VCO. When encoding the MSK, the microphone input signal is muted.
2.3.6.2 Decode
QT/DQT
The output signal from the FM IC (IC400) enters the MCU (IC710) through IC705. IC710 determines whether or not the QT or DQT
matches the preset value, and controls the AFSW and speaker output sounds according to the squelch results.
2-tone
Part of the received AF signal output from the FM IC (IC400) passes through the baseband IC (IC705), and is compared and output
from MOD2 before going to the MCU (IC710). IC710 checks whether or not the 2-tone data is necessary. If it matches, IC710 carries
out a specified operation, such as turning the speaker on.
MSK (Fleet Sync)
The MSK input signal from the FM IC (IC400) goes to IC705. The decoded information is then processed by the MCU.
DTMF
The DTMF input signal from the FM IC (IC400) goes to IC705. The decoded information is then processed by the MCU.
1-10 (No.RA035<Rev.001>)
Selector
IC710
MCU
92
EN4 PTT
39
EN3
Side1
40
EN2
38
EN1 Side2
Fig.8 Key input
PTT
SW
Side1
59
83
Side2
84