SM8521 Datasheet, PDF (36/56 Pages) Sharp Electrionic Components – 8-Bit Single-Chip Microcomputer

SM8521
Compound and Overwrite Mode
To transfer display data, DMA provides two modes.
One is compound mode that source dot data zero
is not stored into the destination. Second is
overwrite mode that any dot data is stored into the
destination.
VRAM
ROM
VRAM
+
VRAM dot data
ROM dot data
ROM dot data = 0 : Transparent
ROM and VRAM
Fig. 17 An Example of Transfer ROM to VRAM in Compound Mode
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