TM-V71A/V71E
10
7-2. Reception Signals
PR9 is the 9600bps data communications reception
output. It sends the FM detection circuit output (RD signals)
through a buffer amplifi er (Q607). These signals are always
output whether the squelch is open or closed.
PR1 is the 1200bps data communications reception
output. It sends the FM detection circuit output (RA signals)
through a buffer amplifi er (Q606). Output is controlled with
the cross point switch (IC806) according to whether squelch
is open or closed.
PR1: The audio signal that was de-emphasised is switched
by the cross point switch and passed through the
electronic volume. The signal is then buffered by Q606
and is sent to the data output terminal. The PR1 signal
is output when squelch is open.
PR9: The signal switched through IC666 is buffered by
Q607 and is sent to the data output terminal.
7-3. Squelch Signal Output Circuit
The squelch circuits is input to the TNC to prevent
c o n f l i c t s f r o m o c c u r r i n g b e t w e e n s i m u l t a n e o u s
receive mode and transmit mode traffic during packet
communications (only during 1200bps). The SQC signal is
output by the MPU (IC918).
The SQC output can be set to the following using the
menu mode.
An initial value is Busy.TX. The logic of the output is Hi
active. The logic of the output can change by MCP-2A.
Menu No.
Display
SQC output type
520
SQC.SRC
OFF/BUSY/SQL/TX/BUSY.TX/SQL.TX
Table 3 SQC output setting
8. Panel Section
The panel section controls serial communications with
the main unit control section, the key input circuit, the
display circuit, and the brightness circuit through the MPU
(IC903).
8-1. Serial Communications Circuit
A buffer IC (IC901, IC902) is used in order to protect the
MPU ports.
8-2. Key, Encoder, Volume Input Circuit
Circuits to operate the panel section keys are connected
to each microprocessor port. The POWER key is pulled up
and the other keys are pulled up within the MPU. Encoder
operating circuits are connected to the MPU and the port is
pulled up. The volume (VOL/SQ) divides the power supply
voltage, reads the A/D port of the MPU, and transfers that
data to the main unit.
8-3. Display Circuit
The MPU controls two LCD drivers (IC906, IC907). It
displays it by connecting IC906 (4 common dots and 39
segment dots) and IC907 (4 common dots and 38 segment
dots) with the LCD.
8-4. Brightness Circuit
The illumination color can be set to either amber or
green. The PWM signal output from the MPU passes
through LPF, is converted into the DC voltage, and controls
the current that fl ows to the LED with the transistor. The
duty of the PWM changes the LED brightness to one of
eight levels or OFF.
Q904
Q902
LPF
SW
Current
control
10V
PWM
AMBER
Q905
Q903
LPF
SW
Current
control
10V
PWM
GREEN
IC903
MPU
Fig. 14 Brightness circuit
CIRCUIT DESCRIPTION