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The selection of the appropriate data pins for passive displays is complicated due to the multiple
driving schemes possible. Active displays do not have such characteristics as dual-scan or double-
pixel mode and, therefore, have much more straight forward selection of the data pins. See
Table 7-2
displays and the use of LCD data pins for specific panels, upper or lower.
Table 7-2. LCD Controller Data Pin Utilization
Color/
Monochrome
Panel
Monochrome
Monochrome
Monochrome
Color
Color
† Double pixel data mode (LCCR0[DPD]=1)
7.3
Schematics/Block Diagram
Refer to
Section 7.5
7.4
Layout Notes
The following design considerations are common to all modes of operation and must be properly
accounted for in any system design in order to have optimal system performance.
7.4.1
Contrast Voltage
Many displays, both active and passive, include a pin for adjusting the display contrast voltage.
This is a variable analog voltage that is supplied to the panel using a voltage source on the system
board. The contrast voltage is adjusted using a variable resistor on the circuit board.
The required voltage range and current capabilities vary among panel manufacturers. Consult the
data sheet for the LCD panel to determine the variable voltage circuit design. Ensure the contrast
voltage is stable; unstable voltage causes visual artifacts. Possible contrast-voltage circuits are
often suggested by panel manufacturers.
®
Intel
PXA27x Processor Family Design Guide
for description of the number of LDD pins required for the various types of passive
Single/
Dual-Scan
Single
Single
Dual
Single
Dual
for the appropriate block diagram for the system under consideration.
Double-Pixel
Screen Portion
Mode
No
Whole
Yes
Whole
Top
No
Bottom
N/A
Whole
Top
N/A
Bottom
LCD Interface
Pins
LDD<3:0>
LDD<7:0>†
LDD<3:0>
LDD<7:4>
LDD<7:0>
LDD<7:0>
LDD<15:8>
II:7-3
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