Module Overview
11-5
LCD Controller
For passive color panels showing 12- or 16-bit color, the data from the frame
buffer is passed directly into the dither logic, bypassing the palette. The three
parallel dither engines then provide up to 3375 colors. The 16-bit color mode
utilizes only the most significant four bits of each color channel. The pixels are
also passed to the panel via an 8-wire interface, 2 2/3 pixels per clock.
For active color panels showing 8-bit color or lower, an entry from the palette
is expanded from 12 bits to 16 bits and passed to the display, providing up to
256 colors out of a possible 4096 (16 x 16 x 16) colors. The pixels are passed
to the panel via a 16-wire interface, 1 pixel per clock.
For active color panels showing 12-bit color, the data is also expanded from
12 bits to 16 bits to provide up to 4096 colors. The pixels are also passed to
the panel via a 16-wire interface, 1 pixel per clock.
For active color panels showing 16-bit color, the data is passed directly to the
display(bypassing palette and dither logic), providing up to 65536 colors. The
pixels are again passed to the panel via a 16-wire interface, 1 pixel per clock.
The active color modes can also be used with an external DAC to drive a video
monitor. The LCD line clock pin functions as a horizontal synchronization
(HSYNC) signal and the frame clock pin functions as a vertical synchronization
(VSYNC) signal.
The pixel clock frequency is derived from the clock provided to the LCD
controller (LCD_CK) from the OMAP5910 clock management logic and is
programmable from LCD_CK/2 to LCD_CK/255 (see Chapter 15, Clock
Generation and System Reset Management). Each time new data is supplied
to the LCD data pins, the pixel clock is toggled to latch the data into the LCD
display serial shifter. The line clock toggles after all pixels in a line have been
transmitted to the LCD driver and a programmable number of pixel clock wait
states have elapsed both at the beginning and end of each line. In passive
mode, the frame clock toggles during the first line of the screen and the begin-
ning and end of each frame are separated by a programmable number of line
clock wait states. Program horizontal front porch (HFP) and horizontal back
porch (HBP) to zero in passive mode.
In active mode, the frame clock is asserted at the end of a frame after a pro-
grammable number of line clock wait states occur. In passive display mode,
the pixel clock does not transition during wait state insertion or when the line
clock is asserted. Finally, the ac-bias (LCD.AC) can be configured to transition
each time a programmable number of line clocks occurs.
Table 11–1 shows details relating to the LCD controller signals.