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13. Dot Matrix LCD Controller (H8/3857 Group)
Read-Modify-Write Mode
In the normal state, the X or Y address is incremented after both read and write accesses to the
display memory. In read-modify-write mode, the address is incremented only after a write, and
remains the same after a read. By using this mode, it is possible to read previously written data,
process that data, and then write it back to the same address.
13.3.7
Scroll Function
The LCD controller allows vertical scrolling of any number of lines to be performed by specifying
the display start line. Figure 13.9 shows the relationship between the display memory and Y
address, and the display memory and LCD display after scrolling, for 1/16 duty and 1/8 duty
settings. If the display start address is set to H'01, the data at Y address H'00 is displayed in the
16th line. Therefore, when the display is scrolled in order to show the next screen, the data at Y
address H'00 must be rewritten with the next display data. This data update should be carried out
after the display is scrolled.
Rev.3.00 Jul. 19, 2007 page 356 of 532
REJ09B0397-0300
START
Set address
Read data
Write data
No
End of modification?
Figure 13.8 Read-Modify-Write Mode Flowchart
(Address) + 1
Yes
END
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