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Viii-2-1
VIII
IVRAM
VIII.2 IVRAM and IVRAM Arbiter
Viii.2.1iVRaM
The S1C33L17 has a built-in 12K-byte RAM (IVRAM) to be used as a video RAM for the LCDC, which is located
at 0x80000 to 0x82FFF in area 3 by default. When the LCDC is not used or when an external SDRAM is used as a
video RAM, IVRAM can be moved to area 0 to use as a general-purpose high-speed RAM. The LCDC provides the
control bit IRAM (D0/0x301A64) for this switch over. Setting IRAM (D0/0x3001A64) to 1 configures the RAM as
a general-purpose RAM in area 0; setting to 0 configures it as a VRAM in area 3.
*iRaM:IRAMAssignmentBitintheIRAMSelectRegister(D0/0x301A64)
Table VIII.2.1.1 lists the differences in the IVRAM function depending on the allocated areas.
TableVIII.2.1.1IVRAMFunctioninDifferentAreas
item
Location
AccessingfromtheLCDC
AccessingfromtheCPU
AccessingbyDMA
UseforVRAM
Programexecution
Storinggeneral-purposedata
Waitcycle
iRaM=0(iVRaM)
Area3,0x80000–0x82FFF
Enabled(viaIVRAMarbiter)
32-bitreadonly
Enabled(viaIVRAMarbiter)
8,16,32-bitread/write
Enabled(viaIVRAMarbiter)
Enabled
Disabled
Enabled
2cyclesmin.
iRaM=1(general-purposeRaM)
Area0,0x2000–0x4FFF*
Disabled
Enabled(direct)
8,16,32-bitread/write
Disabled
Enabled
0cyclesmin.
*Canbeusedasa20KBRAMwithA0RAM
When using IVRAM as a display memory, the memory size required for a screen depends on the screen size and
bpp mode (shades of gray/colors). It can be expressed by the following equation:
Screendatasize=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)
TableVIII.2.1.2IVRAMUsageSamples
Panelsize
320
×240
240
×180
160
×160
Colordepth
1bpp
2bpp
1bpp
2bpp
Datasize
2400words(9600bytes)
1440words(5760bytes)*2
2700words(10800bytes)
800words(3200bytes)
1600words(6400bytes)
usediVRaMrange*1
0x80000–0x8257F
0x80000–0x8167F
0x80000–0x82A2F
0x80000–0x80C7F
0x80000–0x818FF
*1
*2
TheseexamplesassumethatIVRAMisusedfromthebeginning.Thedisplaystart
addresscanbechangedusinganLCDCregister,note,however,thatawordboundary
addressmustbespecified.
Theimagewidthmustbesetinwordunits(=multipleof32/bpppixels).A240-pixelof
imagewidthin1-bppmodecannotbespecifiedinwordunits.Inthiscase,theimagearea
mustbeallocatedtoa256-pixelwidth(theLCDcandisplayimageswitha240-pixelwidth).