
Liquid crystal display controller (LCD)
RM0351
762/1830
DocID024597 Rev 5
COM[
n
]
n
[0 to 7] is active during phase
n
in the odd frame, so the COM pin is driven to
V
LCD
.
During phase
n
of the even frame the COM pin is driven to V
SS
.
In the case of 1/3 or 1/4) bias:
•
COM[
n
] is inactive during phases other than n so the COM pin is driven to 1/3 (1/4)
V
LCD
during odd frames and to 2/3 (3/4) V
LCD
during even frames
In the case of 1/2 bias:
•
If COM[
n
] is inactive during phases other than n, the COM pin is always driven (odd
and even frame) to 1/2 V
LCD
.
When static duty is selected, the segment lines are not multiplexed, which means that each
segment output corresponds to one pixel. In this way only up to 44 pixels can be driven.
COM[0] is always active while COM[7:1] are not used and are driven to V
SS
.
When the LCDEN bit in the LCD_CR register is reset, all common lines are pulled down to
V
SS
and the ENS flag in the LCD_SR register becomes 0. Static duty means that COM[0] is
always active and only two voltage levels are used for the segment and common lines: V
LCD
and V
SS
. A pixel is active if the corresponding SEG line has a voltage opposite to that of the
COM, and inactive when the voltages are equal. In this way the LCD has maximum contrast
(see
). In the
pixel 0 is active while pixel 1 is inactive.
Figure 173. Static duty case 1
In each frame there is only one phase, this is why f
frame
is equal to f
LCD
. If 1/4 duty is
selected there are four phases in a frame in which COM[0] is active during phase 0, COM[1]
is active during phase 1, COM[2] is active during phase 2, and COM[3] is active during
phase 3.
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