ssd1908 Solomon Systech Limited:, ssd1908 Datasheet - Page 141

• Manufacturer Part Number: ssd1908
• Description: Lcd Drivers,lcd Controllers
• Manufacturer: Solomon Systech Limited:

19 Display Rotate Mode
19.1 90° Display Rotate Mode
19.1.1 Register Programming
SSD1908
Figure 19-1 : Relationship Between The Screen Image and the Image Refreshed in 90 ° ° ° ° Display Rotate
Most computer displays are refreshed in landscape orientation – from left to right and top to bottom. Computer
images are stored in the same manner. Display Rotate Mode is designed to rotate the displayed image on an
LCD by 90 ° , 180 ° , or 270 ° in an counter-clockwise direction. The rotation is done in hardware and is
transparent to the user for all display buffer reads and writes. By processing the rotation in hardware, Display
Rotate Mode offers a performance advantage over software rotation of the displayed image.
The image is not actually rotated in the display buffer since there is no address translation during CPU
read/write. The image is rotated during display refresh.
The following figure shows how the programmer sees a 320x480 rotated image and how the image is being
displayed. The application image is written to the SSD1908 in the following sense: A–B–C–D. The display is
refreshed by the SSD1908 in the following sense: B-D-A-C.
Enable 90 ° ° ° ° Display Rotate Mode
Display Start Address
physical memory
start address
Set Display Rotate Mode Select bits to 01 (REG[71h] bits 1:0 = 01).
The display refresh circuitry starts at pixel “B”, therefore the Main Window Display Start Address
registers (REG[74h], REG[75h], REG[76h]) must be programmed with the address of pixel “B”.
To calculate the value of the address of pixel “B” use the following formula (assumes 8bpp color
depth).
Rev 1.0
Main Window Display Start Address bits 16-0
= ((Image address + (panel height x bpp ÷ 8)) ÷ 4) –1
= ((0 + (320 pixels x 8 bpp ÷ 8)) ÷ 4) – 1
= 79 (4Fh)
P 131/131
image seen by programmer
= image in display buffer
A
C
Window
Display
Rotate
320
Oct 2003
B
D
display start address
(panel origin)
Mode.
image refreshed by SSD1908
480
Solomon Systech