Lcd Backlight Control - Micros Systems Workstation 4 LX Service Manual

WS4 Technical Overview
Complex Programmable Logic Device (CPLD)
LCD Backlight Control (REF: AB28/ABRD36 - Sheet 17)
The CPLD provides LCD Backlight Control as shown in Figure 2-18 below.
Pulse Width Modulation (PWM) Brightness Control
Table 2-2 summaries the pre-selected PWM values for the standard Dim,
Normal, and Bright backlight settings available through the WS4 API.
The PWM values from the CPU create a pulse of varying widths to modulate
the backlight inverter module attached to the LCD panel. The backlight
brightness values are hard coded in the boot loader and optimized for the
supported TFT LCD panel.
+10.4V Regulator (Sheet 17)
This circuit regulates +12V to +10.4V for the Backlight Inverter Board
mounted to the LCD bracket in the top cover. This voltage regulator is
required to prevent momentary dimming of the LCD backlight when a cash
drawer solenoid fires.
+12V Always is fed through poly fuse F5 to Q19 which produces +10.4V and
is routed to backlight connector J17 at pins 4 and 5.
2-30
Figure 2-18: Backlight Brightness Control
PWM Value % Brightness
00
41
60
75
Table 2-2: Backlight Brightness Values
Backlight
Mode
0 OFF
55 DIM
60 Normal
100 Bright
Workstation 4 and 4 LX Field Service Guide