TM-271A/271E
5
Control Circuit
The CPU carries out the following tasks (See Fig. 10.):
1) Controls the WIDE, NARROW, TX/RX outputs.
2) Adjusts the AF signal level of the AF filter (IC251) and
turns the filter select compounder on or off.
3) Controls the display unit.
4) Controls the PLL (IC401).
5) Controls the D/A converter (IC161) and adjusts the vol-
ume, modulation and transmission power.
■
Memory Circuit
The transceiver has an 64k-bit EEPROM (IC66). The
EEPROM contains adjustment data. The CPU (IC101) con-
trols the EEPROM through three serial data lines. (See Fig.
11.)
IC161
D/A
converter
IC401
PLL
IC101
CPU
LD
DT
CK
PLLE
EEPCK
IC101
CPU
IC66
EEPROM
EEPSDT
EEPWP
■
Display Circuit
The CPU (IC101) controls the display LCD and LEDs.
When power is on, the LCD driver will use the BL line to con-
trol the LCD illumination and key backlight LEDs.
The brightness function is controlled by the switch Q12.
The LCD driver (IC3) and CPU (IC101) communicate through
the CE, CL, DI, DO lines. (See Fig. 12.)
■
Key Matrix Circuit
The TM-271 front panel has function keys. Each of them
is connected to a cross point of a matrix of the KI1 to KI3 and
KSI to KS2 ports of the LCD driver.
The LCD driver monitors the status of the KI1 to KI3 and
KS1 to KS2 ports. If the state of one of the ports changes,
the LCD driver assumes that the key at the matrix point corre-
sponding to that port has been pressed.
■
Encode
The DCS and CTCSS 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 pin of the CPU and 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 MOD level and the
balance between the MOD and CTCSS/DCS levels. Part of a
CTCSS/DCS signal is summed with MOD 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 modula-
tion.
IC3
LCD
driver
KI1
KI2
KI3
KS2
KS1
FUNC
REV
CALL
VFO
MR
MHz
(Encoder)
X401
TCXO
IC161
D/A
VCO
IC203
SUM
AMP
IC203
SUM
AMP
IC401
PLL
TCXO
MOD
VCO
MOD
Amp
DI
QT/DQT
(CPU1)
DTMO
(EVOL15)
IC101
CPU
TONE
DTMF
Fig. 10
Control circuit
Fig. 11
Memory circuit
Q10
SW
Q6
SW
IC101
CPU
D2~D4
Q9
SW
D19~D30
Q12
SW
IC3
LCD
driver
CE
CL
DI
DO
BL
COM0~
COM3
SEG0~
SEG30
LCD
BRI
Fig. 12
Display circuit
Fig. 13
Key matrix circuit
Fig. 14
Encoder
CIRCUIT DESCRIPTION