HD66420 Datasheet, PDF (26/52 Pages) Hitachi Semiconductor – (RAM-Provided 160 Channel 4-Level Grey Scale Driver for Dot Matrix Graphics LCD)

HD66420
Read-Modify-Write: X- or Y-address is incremented after reading form or writing data to the display
RAM at normal mode. However, X- or Y-address is not incremented after reading data from the display
RAM at read-modify-write mode. The data which is read from the display RAM may be modified and
written to the same address without re-setting the address. Data is temporarily latched into a HD66420’s
buffer and then output next time a read is performed in a subsequent cycle. This means that the dummy
read is necessary after every cycle. This sequence is shown in figure 14.
START
Set X-address
Set Y-address
dummy read
Read Data
Write Data
Address
incremented
no
Finish Modifying
yes
END
Figure 14 The Flow Chart for Read-Modify-Write
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