Kenwood NX-840, Service Manual

Page: 13 / 54

(No.RA011<Rev.001>)1-13
2.4.5 Control Circuit
The MCU carries out the following tasks:
(1) Controls the FM IC (IC501).
(2) Controls the baseband IC (IC709).
(3) Controls the PLL (IC2) & TX/RX outputs.
(4) Controls IO expender through I2C level converter.
(5) Controls the display unit.
Fig.8 Control circuit
2.4.5.1 Memory Circuit
The transceiver has an 256k-bit EEPROM (IC716). The EE-
PROM contains adjustment data. The MCU (IC714) controls the
EEPROM through three serial data lines.
Fig.9 Memory circuit
2.4.5.2 Display Circuit
The MCU (IC714) controls the Display 7-segment LED and
LEDs.
When power is on, the MCU will use the MBL line to control the
key backlight LEDs.
When the transceiver is busy, the GLED line goes high, Q1 turns
on and the green LED (D23) lights after Q4 turn on. In transmit
mode, the RLED line goes high, Q2 and Q8 turns on and the red
LED (D23) lights.
BLED will be set high when the function select (FPU setting) is
on, Q6 turn on and the blue LED (D22) lights.
The dimmer function is controlled by the switch Q5. The LED
driver (IC1) controls the functions of the 7-segment LED through
the LEDI, LECE, LECL, LELH lines from the MCU.
Fig.10 Dsplay circuit
BLED
C.DATA
R.DATA
SCLK
IRQ
CSN
IC700 IC702
Display unit
IC1
LED Driver
IC714
MCU
IC709
Baseband
IC
IC501
FM IC
RLED GLED MBL
LECI LECE LECL LELH
IC2
PLL IC
PLL_U PLL_CLK PLL_DATA PLL_LE PLL_PDN2
PDN
RSTN
CSN
SCLK
SDATA
I
2
C level
converter
IO
expender
EEP_DATAO
EEP_CLK
EEP_DATAI
EEP_CS
EEP_WP
IC716
EEPROM
IC714
MCU
Q4
SW
Q3
SW
Q5
SW
D1~D5
Key backlight
Display
7-segment
IC714
MCU
IC1
LED
driver
LEDI
LEDM
LECE
LECL
LELH
MBL
Q1
SW
Q7
SW
D23
GLED
Q2
SW
Q8
SW
RLED
Q6
SW
D22
BLED