Intel® PXA26x Processor Family Developer’s Manual 7-9
Liquid Crystal Displa y Controller
7.3.4 Output FIFOs
The LCD controller has two output FIFOs to queue pixel data before it is se nt to the pins. Each
output FIFO is 16 bytes, organized as 16 entries by 8-bits wide. Pix el values are accumulated in a
serial shifter and written to the FIFO buffers in 4-, 8-, or 16-bit quantities. Pins used are:
Four pins for single-panel monochrome screens
8 pins for single- and dual-panel monochrome screens and single-panel color displays
16 pins for dual-panel color and active displays.
Each time a value is taken from the bottom of the FIFO, the entry is invalidated, and all data in the
FIFO moves down one pos ition.
7.3.5 Liquid Crystal Display Controller Pin Usage
See also Table7-1 , “Pin Descriptions” on p age 7-4.
The timing of the line (L_LCLK) and frame (L_FCLK) clocks is programmable to support both
passive display and active display modes. Programming options include:
Wait state insertion at the beginning and end of each line and frame
Pixel clock (L_PCLK)
Line clock (L_LCLK)
Frame clock (L_FCLK)
Output enable signal polarity
Frame clock pulse width.
See Section7.5, “Functional Timing” for pin timing diagrams. When the LCD controller is
disabled, all of its pins can be used for GPIO. See Chapter4, “System Integration Unit” for further
details.
7.3.5.1 Passive-Display Timing
In passive display mode (LCCR0[P AS]=0 ), L_ PCLK to ggl es on ly whe n d ata is bei ng wr itten t o t he
panel. When an entire line of pixels has been sent to the display, L_LCLK is asserted. When an
entire frame of pixels has been sent to the display, L_FCLK is asserted.
If an output FIFO underrun occurs ( i.e., the LCD controller runs out o f data), L_PCLK stalls until
valid data is available. This results in a slower pixel clock, but data sent to the display is always
valid.
To prevent a DC charge from build ing wi thi n a p assive d is play, its power and ground supplies must
be switched periodically. Many modern panel s do this autom ati cally. If not, the LCD controller can
toggle the AC bias pin (L_BIAS) to signal the display to switch pol a rity. The frequency of the
L_BIAS toggle is controlled by programming the number of line clock transitions between each
toggle (LCCR3[ACB]).