TK-90
29
The VOX circuit gives priority to what goes over a speci-
fied value by the use of a flip-flop IC (IC601). Setting values
are set for the speaker output and microphone input levels
separately. The level which first exceeds the threshold is
given priority.
If input from microphones exceeds the level set in the
VOX sensitivity before output from speakers exceeds the
specified value set in the anti-VOX sensitivity, transmission
status is yielded. Even if the input from the microphone be-
comes less than the VOX sensitivity, the transmission condi-
tion is maintained for the delay time.
When sound is output from the speakers and the output is
more than the anti-VOX specified value, the setting can be
made so that the status is not changed to transmission even
with any amount of input into the microphone, or so that VOX
does not activate with the sound of transceiver itself.
The VOX delay time is set and controlled by the MCU soft-
ware.
3) DI Circuit
This is an external input circuit for when modulating signal
other than from the microphone terminal, such as when us-
ing the optional KCT-39. The sensitivity is the same as a mi-
crophone, but because a trimmer potentiometer (VR852) is
included for input, it can therefore support a wide range of
input levels.
Digital Control Circuit
■
Outline
The digital control circuit consists of the main MCU at its
center, the EEPROM (IC854), and the reset IC (IC856 and
IC857). (Please refer to the block diagram.)
■
Main MCU
The main MCU (IC855) operates at a power supply voltage
of 5V and a clock frequency of 11.0592MHz. The EEPROM is
connected to the main MCU for backup. The power supply
voltage monitoring circuit including the reset circuit are also
connected.
CIRCUIT DESCRIPTION /
!
KCT-31
IC856
Reset circuit /
复位电路
IC857
Reduced voltage detection circuit /
压降检测电路
Q856
Over voltage detection circuit /
过压检测电路
VGS-1
KCT-39
X851
X’tal (11.0592MHz)
Panel MCU
External AT
IC855
Main MCU
(built-in flash)
IC854
EEPROM
KPE-2
面板MCU
外部AT
主MCU (内置闪存)
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