TH-D72A/D72E
11
8. Control System
8-1. RESET, BACKUP circuit
When the suB voltage falls, and the 33M voltage
is detected to be lower than the threshold voltage of the
RESET IC (IC726), the connected Main MCU (IC737) detects
this with the interrupt terminal (/RST), backs up the data to
the EEPROM ICs (IC730,IC731), and turns off the power.
8-2. LCD, LED, KEY circuit
The LCD Display is controlled by the driver built into the
Main MCU (IC737). The contrast is adjusted by the regulator
IC (IC701), similarly controlled by the LCDCNT signal from
the Main MCU (IC737).
On the other hand, the LEDs (D710~715, D718~724) for
the LCD and 16 KEY backlight are lit by the LAMP B power
supply through the DC switches (Q721, Q722). The port of
the Main MCU (IC737) corresponding to the 16 KEY is com-
posed of a 5x5 matrix and detects a pressed KEY by scan-
ning in the software.
8-3. INT-GPS control
The GPS unit installed in the equipment communicates
directly with the Main MCU (IC737) and is controlled. The in-
ternal GPS power supply changes with the DC switch (Q701)
controlled by the Main MCU (IC737).
8-4. RTC function
The RTC IC (IC717) that operates with the lithium battery
has a clock function.
8-5. PC port
It corresponds to the connection to the external instru-
ment (PC) through the USB connector.
8-6. COM port
To correspond to the connection with the external GPS
equipment, it communicates by switching ICs (IC708,
IC709) by the Main MCU (IC737) / TNC MCU (IC727) and
the RS232C driver IC (IC702).
Figure 7 Control circuit
IC702
RS232C
driver
J702
TXD
RXD
COM
port
SW IC
IC709
USB
driver
IC710
V cont
IC701
IC703
RESET
IC
IC726
RTC IC
IC717
X701
EEPROM
IC730,IC731
Regulator
IC
Vbus
SW
SW IC
IC708
232B_S
SKY_SW
RXD_COM
TXD_COM
TXD_EGPS
RXD_EGPS
DC
SW
DC
SW
Q704
33C
J703
PC
port
IC736
Vbus_USB
LAMP
LCD
LCD
DC
SW
DC
SW
Q722
Q721
LAMP B
Backlight
LED
/RST
RXD_IGPS
TXD_IGPS
GP_ON
GP_PS
VGPS
Q701
33C
INT_GPS
33M
IC737
Main
MCU
TNC
MCU
IC727
CIRCUIT DESCRIPTION