NEC uPD72257, Preliminary User'S Manual

Page: 208 / 343

7.7.2.5 VOnLCDUPBASE - Framebuffer base address register
This register defines the framebuffer base address of the frame to be output.
VOnLCDUPBASE holds a byte address, thus the lower two bits must be 00
B
due
to 32-bit alignment in the framebuffer.
Upon output start of a new display data frame, VOnLCDUPBASE is copied to the
current framebuffer address register VOnLCDUPCURR, which is effectively used
for addressing the framebuffer during frame output. The copy process goes along
with the generation of the LCD next base address update interrupt VOnNBAINT.
Caution
Before rewriting this register make sure that the previous address is effectively
in use and can be overwritten. Therefore wait for the occurence of the
VOnNBAINT before rewriting this register.
Access This register can be read/written in 32-bit units.
Address <VOn_Base> + 010
H
Initial Value 0000 0000
H
. This register is initialized by any reset.
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
LCDLPBASE[31:16]
R/W
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
LCDLPBASE[15:2] 0 0
R/W R R
Bits marked as read-only must be written with "0", reading returns undefined
values.
Bit Bit name Function
31 to 2
LCDUPBASE
[31:2]
LCDUPBASE[31:0] is the start address of the frame data in memory.
The lower bits LCDUPBASE[1:0] are 00
B
due to 32-bit word alignment.
Chapter 7 Video Output
208
Preliminary User's Manual S19203EE1V3UM00