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S1C88650 TECHNICAL MANUAL
EPSON
113
5 PERIPHERAL CIRCUITS AND THEIR OPERATION (LCD Driver)
5.11.5 Display memory
The S1C88650 has a built-in 768-byte display
memory. The display memory is allocated to
address Fx00H–Fx7FH (x = 8–DH) and the corre-
spondence between the memory bits and com-
mon/segment terminal is changed according to
the selection status of the following items.
(1) Drive duty (1/32, 1/16 or 1/8 duty)
(2) Dot font (16
×
16/5
×
8 or 12
×
12 dots)
(3) SEG terminal assignment (normal or reverse)
When 1/16 or 1/8 duty is selected for the drive
duty, two screen areas are reserved in the display
memory and the area to be displayed can be
selected by the display memory area select register
DSPAR. When "0" is written to DSPAR, display
area 0 is selected and when "1" is written, display
area 1 is selected.
Furthermore, memory allocation for 16
×
16/5
×
8
dots and 12
×
12 dots can be selected in order to
easily display 12
×
12-dot font characters on the
LCD panel.
This selection can be done by the dot font selection
register DTFNT: when "0" is written to DTFNT, 16
×
16/5
×
8 dots is selected and when "1" is written,
12
×
12 dots is selected.
The memory allocation for the SEG terminals can
be reversed using the SEG assignment reverse
register SEGREV.
Table 5.11.5.1 Selecting SEG assignment
SEGREV
1
0
Assignment
Reverse
Normal
Fx00H
SEG125
SEG0
Fx70H
SEG0
SEG125
The correspondence between the display memory
bits set according to the drive duty and font size,
and the common/segment terminals are shown in
Figures 5.11.5.1–5.11.5.6.
When "1" is written to the display memory bit
corresponding to the dot on the LCD panel, the
dot goes ON and when "0" is written, it goes OFF.
Since display memory is designed to permit
reading/writing, it can be controlled in bit units
by logical operation instructions and other means
(read, modify and write instructions).
The display area bits which have not been as-
signed within the 768-byte display memory can be
used as general purpose RAM with read/write
capabilities. Even when external memory has
expanded into the display memory area, this area
is not released to external memory. Access to this
area is always via display memory.