TK-7108
30
■
Key Matrix Circuit
The TK-7102 front panel has function keys. Each of them
is connected to a cross point of a matrix of the KMI1 to KMO2
ports of the microprocessor. The KMO1 to KMO2 ports are
always high, while the KMI1 to KMI4 ports are always low.
The microprocessor monitors the status of the KMI1 to
KMO2 ports. If the state of one of the ports changes, the
microprocessor assumes that the key at the matrix point cor-
responding to that port has been pressed.
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IC101
CPU
KMI1
KMI2
KMI3
KMI4
KMO1
KMO2
↑
↓
1
2
3
P
M
4
X401
TCXO
IC161
D/A
VCO
IC203
SUM
AMP
IC203
SUM
AMP
IC161
D/A
IC401
PLL
TCXO
MOD
VCO
MOD
HT
DI
QT/DQT
DTMF
IC101
CPU
IC101
CPU
SIGNAL
W/NO (EVOL2)
88
CIRCUIT DESCRIPTION /
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■
Encode
The QT and DQT signals are output from QT/DQT of the
CPU (IC101) and summed with the external pin DI line by the
summing amplifier (IC203) and the resulting signal goes to
the D/A converter (IC161). The DTMF signal is output from
DTMF of the CPU and goes to the D/A converter (IC161). The
signal is summed with a MIC signal by the summing amplifier
(IC203), and the resulting signal goes to the D/A converter
(IC161).
The D/A converter (IC161) adjusts the MO level and the
balance between the MO and QT/DQT levels. Part of a QT/
DQT signal is summed with MO and the resulting signal goes
to the VCOMOD pin of the VCO. This signal is applied to a
varicap diode in the VCO for direct FM modulation.
■
Decode
• QT/DQT/DTMF
The signal (W/NO (EVOL2)) goes to SIGNAL (pin 88) of
CPU (IC101). The QT/DQT signal will pass through the low-
pass filters in the CPU (IC101) and be decoded within the
CPU (IC101). The DTMF signal will be decoded within the
CPU (IC101).
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Fig. 13
Key matrix circuit /
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Fig. 14
Encode /
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Fig. 15
Decode /
NR
