Back-Lite Control Circuit - Panasonic JS-170FR Series Service Manual

2.1.7.3

Back-Lite control circuit

A cold-cathode tube is used for the back light of the LCD.
The +12V power supply for driving is fed from an external inverter.
Assuming that the LCD is in the display mode (the FPEN signal at the high level), ON/OFF control of the power supply is
effected by software.
This system performs controls in two positions; GPO_0 (Default = High) that is a general-purpose port of the FW82371EB and
Bit0 (BACKEN) that is the I/O address 320H.
The Back-Lite is turned ON when the conditions of both are satisfied.
Generally, the control of FW82371EB is not used. Instead, ON/OFF control is performed by managing the BACKEN signal that is
used for the control of the I/O address 320H.
The control hardware is located inside the gate array.
G AT E A R AY
84
BACK_ON
B L _ON
85
FPEN
F P E N _IN
86
FPVDDEN
L C D P W R
87
FP/FVSYNC
V S Y N C
83
B A C K L I T O N
2-34
+12V
+12V
GND
BACKLIT_ON#