hd66420 Renesas Electronics Corporation., hd66420 Datasheet - Page 26

• Manufacturer Part Number: hd66420
• Description: Ram-provided 160 Channel 4-level Grey Scale Driver For Dot Matrix Graphics Lcd
• Manufacturer: Renesas Electronics Corporation.

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.
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Figure 14 The Flow Chart for Read-Modify-Write
Finish Modifying
Set X-address
Set Y-address
dummy read
Read Data
Write Data
START
END
yes
no
Address
incremented