Kenwood TK-782 Service Manual page 41

TK-782
" Key Matrix Circuit
The TK-782 front panel has ten keys. Each of them is
connected to a cross point of a matrix of the KEY1 to KEY7
ports of the microprocessor. The KEY5 to KEY7 ports are
always high, while the KEY1 to KEY4 ports are always low.
The microprocessor monitors the status of the KEY1 to
KEY7 ports. If the state of one of the ports changes, the
microprocessor assumes that the key at the matrix point
corresponding to that port has been pressed. Unused points
(KEY1 to KEY7) are also used for foot switch (FSW) input.
"
VOL
UP
KEY7
MONI
KEY6
KEY5
IC511 KEY4 D
CPU
KEY3
KEY2
KEY1
Fig. 12 Key matrix circuit /
" Encode
The QT, DQT signals are output from LSDO of the CPU
(IC511) and go to the D/A converter (IC5) of the TX-RX unit (A/
2). The DTMF and single/5-tone signals are output from HSDO
of the CPU and goes to the audio processor (IC504). An MSK
signal is output from the audio processor according to the
data (AFDAT) from the CPU. The signal is summed with a
MIC/MSK signal by the audio processor (IC504), and the re-
sulting signal passes through an analog switch (IC506) and
goes to the TX-RX unit (A/2) (MO).
MO is summed with the external pin DI line by the sum-
ming amplifier (IC3) and the resulting signal goes to the D/A
converter (IC5). The D/A converter (IC5) adjusts the MO level
and the balance between the MO and TO levels. Part of a TO
signal is summed with an output signal from pin 3 (MO) of
IC5 and the resulting signal goes to the MD pin of the VCO.
This signal is applied to a varicap diode in the VCO for direct
FM modulation.
40
CIRCUIT DESCRIPTION /
FSW
VOL
Q511
DOWN
A B C
SCAN CH CH
DOWN UP
"
LSDO
MIC
IC511
CPU
AFDAT
IC504 IC506
HSDO Audio Analog
processor SW
Fig. 13 Encode /
" Decode
The signal (DEO) detected by the TX-RX unit (A/2) passes
through two low-pass filters of IC501, goes to LSDI of the
CPU (IC511) to decode QT, DQT. The DTMF signal is de-
coded by a dedicated IC (IC507) and the resulting signal is
sent to the CPU (IC511) as serial data (STD).
"
IC501(2/2)
LPF
LSDI
IC511
CPU
IC507
STD
DTMF
DECO.
Fig. 14 Decode /
TX-RX UNIT (A/2)
TO MB
X1 IC300
VCXO PLL
DI
MD
IC5 A1
IC3
D/A
VCO
MO
SUM
AMP
IC501(1/2)
LPF
DEO
HT