Specifications

Hardware Configuration
2–37
2.11.3 The LCD Bias Supply Option
The LCD Bias Supply Option is a small circuit board that supplies Vee power to an LCD display. The
board converts the +5V from the Little Board/P5i to the Vee voltage (between 15V and 35V) required by
most LCD panels, and makes this voltage available on the flat panel connector J3.
LCD displays are sensitive to the sequence (order) and timing that power supply and control signals are
applied to the display during power up and removed during power down cycles. LCD manufacturers
warn OEMs that violating the sequence and timing specifications of these signals can damage the display
or reduce its service life. The Little Board/P5i video controller automatically sequences the appropriate
signals to meet the requirements of virtually any LCD display.
The Ampro LCD Bias Supply option mounts parallel to the Little Board/P5i, connected to the board via a
12-pin connector, J4. You secure the board to the Little Board/P5i using a 7/16 inch nylon standoff.
Table 2–30 shows the connector pinout for J4, with a description of each signal. Note that some signals
also appear on the flat panel connector, J3.
Table 2–30 LCD Bias Supply Option Connector (J4)
J4 Pin J3 Pin Description
1 Ground
2 +5V to the Vee Supply Option board
4 Ground
6 38 Enable Vee
TTL control signal, driven by the VGA controller
chip
8 Ground
11 46 Vee Output, to panel
12 47 Contrast adjustment
Analog control signal
Selecting Vee Polarity
Most LCD displays require a Vee supply of between 15V and 35V. Some panels need a negative supply,
and some a positive supply. The LCD Bias Supply Option provides a jumper for selecting the Vee output
polarity. To select the polarity for the panel you will be using, set the jumper on W1 (on the LCD Bias
Supply board, not on the Little Board/P5i) as shown in Figure 2–9.
Figure 2–9 Vee Polarity Selection Jumper