HD66421 Datasheet, PDF (24/46 Pages) Hitachi Semiconductor – (RAM-Provided 160 Channel 4-Level Grey Scale Driver for Dot Matrix Graphics LCD)

Preliminary
Rev. 1.1E '99.02.10
HD66421
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 HD66421'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 18.
START
Set X-address
Set Y-address
dummy read
Read Data
Write Data
Address
incremented
no
Finish Modifying
yes
END
Figure 18 The Flow Chart for Read-Modify-Write
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