Circuit Description - Kenwood RC-2000 Service Manual

RC-2000
Panel Section (LCD ASSY : B38-0829-05)
The panel section controls serial communications with
the main unit control section, the key input circuit, the dis-
play circuit, and the dimmer circuit through the microproces-
sor (IC4).
Serial communications circuit
A buffer amp is inserted in order to protect the micropro-
cessor ports.
Key, Volume input circuit
Circuits to operate the panel section keys are connected
to each microprocessor port. The PSW key is pulled up and
the other keys are pulled up with software within the micro-
processor. Rotary encoder operating circuits are connected
directly to the microprocessor. The control divides the
power supply voltage, reads the A/D port of the micropro-
cessor, and transfers that data to the main unit.
Display circuit
Display section is a 188 x 54-dot full-dot matrix LCD con-
trolled by two LCD. As shown is Figure 1, the master IC
(IC2) side is connected to 22 common dots and 88 segment
dots and the slave IC (IC1) side is connected to 33 common
dots and 100 segment dots. The LCD drive voltage is ob-
tained by raising the power supply voltage (5V) within the IC.
22
COM
88
SEG
LCD
Driver
IC2
Fig. 1 Display circuit
2

CIRCUIT DESCRIPTION

LCD
188 × 54 (dot)
33
COM
100
SEG
LCD
Driver
IC1
Microprocessor
IC4
X54-329
Dimmer circuit
The dimmer circuit switches the lamp brightness to one
of four levels or OFF (See table1). The current flowing to the
LEDs is varied by selecting resistors from R8 to R14.
Dimmer level DIM 0
1 H
2 L
3 L
4 L
OFF L
Table 1 Port logic
IC4
Microprocessor
R13
DIM3 Q8
R14
R11
Q7
DIM2
R12
Q6
DIM1
Q5
Q4
R10
Q3
R8
DIM0
Q2
Fig. 2 Dimmer circuit
DIM 1 DIM 2 DIM 3
L L L
H L L
L H L
L L H
L L L
LCD ASSY
9V
R9