Specifications

Hardware Configuration
2–35
2.12.3 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/486i 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 LCD Bias Supply option, in conjunction with
control signals from the Little Board/486i video controller option, 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/486i, connected to the board
via a 12-pin connector, J4. You secure the board to the Little Board/486i using a .6 inch standoff.
The table below shows the connector pinout for J4, with a description of each signal. Note that some
signals also appear on the flat panel connector, J3.
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
Table 2-26 LCD Bias Supply Option Connector (J4)
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/486i) as shown in the following figure.