User Manual

9-4 EP7309/11/12 User’s Manual - DS508UM4

LCD Interface

Latency and access time s w ill need to be calculated prior to selecting an LC D panel to

guarantee available bandwidth for the rest of th e system. It should be noted that the

refresh rate is not affected b y the total n umber of pixels.

Gray Scale

The figure below shows the organization of the video map for all bits-per-pixel

combinations. As seen the in th e diagram, the gray scale b locks represent th e two 32-

bit palette registers. Each palette register represents eight 4-bit nibbles for a total of 16

nibbles.

Gray scale creates an intensity for each of the pixel values stored in memory. Four

bits-per-pixel corresponds to a theoretical color depth of 16. Two bits-per-pixel

corresponds to a c olor depth of fou r and so on. Since gray s cale values 7 and 8 create

the same intensity, the actual color depth for 4bpp is 1 5. The effect is created by

simply controlling the amount of time the pixel remains on. See the Gray scale value

to Color Mapping diagram for more details.

An exam ple of this would be the value 12, th at i s stored in a n ibble in the framebuffer

memory. If the 4 bpp is programmed into the controller, the value 12 is map ped to the

LCD palette register for g ray scale value for pixel value 12, assuming a one-to-one

correspondence between the number 12 in memory, and the intensity (Gray scale

value), this pixel will have a duty cycle of about 11/15 or will be lit approximately

73.3% of the time.

Programming the controller includes the following

• LCDCON: Configuration interface for a specific LCD panel

• PALLSW /PALM SW: Sets the palette registers

• FBADD R: Sets the start location in sy stem mem ory for the LCD frame

buffer

• SYSCON1: LCDEN bit turns LCD controller on (enabled).

Note: LCD controller must not be enabled until the above registers are programmed.