NEC Barracuda, Service Manual

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Barracuda PDA Maintenance
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Depending on the type of panel used, the LCD controller is programmed to use either 4-, 8-, or 16-pixel data
output pins. Single –panel monochrome displays use either four or eight data pins to output 4 or 8 pixels for each
pixel clock; single-panel color displays use eight pins to output 2-2/3 pixels each pixel clock ( 8 pins / 3 colors /
pixel = 2-2/3 pixels per clock ). The LCD controller also supports dual-panel mode, which causes the LCD
controller’s data lines to be split into two groups, one to drive the top half and one to drive the bottom half of the
screen. For dual-panel displays, the number of pixel data output pins is doubled, allowing twice as many pixels
to be output each pixel clock to the two halves of the screen.
In active color display mode, the LCD controller can drive TFT displays. The LCD’s line clock pin functions as a
horizontal sync ( HSYNC ) signal, the frame clock pin functions as a vertical sync ( VSYNC ) signal, and the ac
bias pin functions as an output enable ( OE ) signal. In TFT mode, the LCD’s dither logic is bypassed, sending
sending selected palette entries ( 12 bits each ) directly to the LCD’s data output pins. Additionally, 16-bit pixels
can be used that bypass both the palette and the dither logic.
The LCD controller can be configured in active color display mode and used with an external DAC ( and
optionally an external palette ) to drive a video monitor. Note that only monitors that implement the RGB
data format can be used; the LCD controller does not support the NTSC standard .
When the LCD controller is disabled, control of its pins is given to the peripheral pin controller ( PPC ) to
be used as general-purpose digital input/output pins that are noninterruptible. The LCD controller’s pins
include:
LDD 7:0
Data lines used to transmit either four or eight data values at a time to the LCD display. For
monochrome displays, each pin value represents a pixel; for passive color, groupings of three
pin values represent one pixel ( red, green, and blue data values ). In single-panel monochrome
mode, LDD 3:0 pins are used. For double-pixel data, single-panel monochrome, dual-panel
monochrome, single-panel color, and active color modes LDD 7:0 are used.