26 LCD CONTROLLER (LCDC)
S1C33L26 TECHNICAL MANUAL
Seiko Epson Corporation
26-5
System Settings
26.4
Configuration of Display Data Memory (VRAM)
26.4.1
The S1C33L26 has a built-in 20K-byte display data memory (IVRAM). This memory allows selection whether it is
used as a VRAM by locating at 0x90000 to 0x94fff in Area 3 or a general-purpose RAM by locating in Area 0. Set-
ting IVRAM_LOC/MISC_IRAM_LOC register to 0 configures the IVRAM as a general-purpose RAM in Area 0;
setting to 1 configures it as a VRAM in Area 3. At initial reset, this memory is located in Area 3 as a VRAM allow-
ing LCDC to access directly.
The LCDC can use an external SDRAM/SRAM as a VRAM in addition to IVRAM (the external SDRAM/SRAM
can store general-purpose data as well as display data). There is no special configuration procedure for use of the
external VRAM. Furthermore, both the external SDRAM/SRAM and IVRAM can be used as a VRAM simultane-
ously. The LCDC handles two screen data for the main window and the sub-window overlaid over the main window
to support “Picture-in-Picture Plus.” Also the LCDC can switch the display by selecting a screen from two or more
display data prepared in the VRAM. Since the display start memory address is specified using a register, display
data can be stored in any location (but it must be a word boundary address) in the memory.
Figure 26.4.1.1 shows memory usage examples.
IVRAM
SDRAM
Window
Main
Sub
When using Picture-in-Picture Plus
IVRAM
SDRAM
Window
Main
Sub
IVRAM
SDRAM
Window
Main
Sub
IVRAM
SDRAM
Window
Main
Sub
Not
used
Ex. 1
IVRAM
SDRAM
Window
Screen 1
Window
Screen 2
When switching screens
Ex. 5
Ex. 2
Ex. 3
Ex. 4
SDRAM
Virtual screen
Actual display window
When using virtual screen area
Ex. 7
IVRAM
SDRAM
Window
Screen 1
Window
Screen 2
Ex. 6
Not
used
SDRAM
Virtual screen
Actual display window
4.1.1 Memory Usage Examples
Figure 26.
The memory size required for a screen depends on the screen size and bpp mode. It can be expressed by the follow-
ing equation:
Screen data size = H_PIXEL
×
V_PIXEL
×
bpp / 32 [words]
(The fractional portion of the number must be rounded up.)
H_PIXEL: Number of horizontal pixels
V_PIXEL: Number of vertical pixels
bpp:
Number of bits per pixel (1, 2, 4, 8, 12, 16, 24)
For example, a 320
×
240-pixel screen displayed in 64K colors (16-bpp mode) needs a 38,400 words (150K bytes)
of memory area.