Samsung S3C2440A - Manual (Page 411)

S3C2440A RISC MICROPROCESSOR LCD CONTROLLER
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Gray Level Selection Guide
The S3C2440A LCD controller can generate 16 gray level using Frame Rate Control (FRC). The FRC
characteristics may cause unexpected patterns in gray level. These unwanted erroneous patterns may be shown
in fast response LCD or at lower frame rates.
Because the quality of LCD gray levels depends on LCD's own characteristics, the user has to select an
appropriate gray level after viewing all gray levels on user's own LCD.
Select the gray level quality through the following procedures:
1. Get the latest dithering pattern register value from SAMSUNG.
2. Display 16 gray bar in LCD.
3. Change the frame rate into an optimal value.
4. Change the VM alternating period to get the best quality.
5. As viewing 16 gray bars, select a good gray level, which is displayed well on your LCD.
6. Use only the good gray levels for quality.
LCD Refresh Bus Bandwidth Calculation Guide
The S3C2440A LCD controller can support various LCD display sizes. To select a suitable size (for the flicker free
LCD system application), the user have to consider the LCD refresh bus bandwidth determined by the LCD display
size, bit per pixel (bpp), frame rate, memory bus width, memory type, and so on.
LCD Data Rate (Byte/s) = bpp x (Horizontal display size) x (Vertical display size) x (Frame rate) /8
LCD DMA Burst Count (Times/s) = LCD Data Rate(Byte/s) /16(Byte) ; LCD DMA using 4words(16Byte) burst
Pdma means LCD DMA access period. In other words, the value of Pdma indicates the period of four-beat burst
(4-words burst) for video data fetch. So, Pdma depends on memory type and memory setting.
Eventually, LCD System Load is determined by LCD DMA Burst Count and Pdma.
LCD System Load = LCD DMA Burst Count x Pdma
Example 3:
640 x 480, 8bpp, 60 frame/sec, 16-bit data bus width, SDRAM (Trp=2HCLK / Trcd=2HCLK / CL=2HCLK) and
HCLK frequency is 60 MHz
LCD Data Rate = 8 x 640 x 480 x 60 / 8 = 18.432Mbyte/s
LCD DMA Burst Count = 18.432 / 16 = 1.152M/s
Pdma = (Trp+Trcd+CL+(2 x 4)+1) x (1/60MHz) = 0.250ms
LCD System Load = 1.152 x 250 = 0.288
System Bus Occupation Rate = (0.288/1) x 100 = 28.8%