LCD controller drive signals

AN3114

14/43

Doc ID 16829 Rev 3

Discrimination ratio calculation for quadruplex mode:

COM3 - SEG0 [ON] = (2VDD/3 - VDD/3) + (2VDD/3 - VDD/3) + (2VDD/3 - VDD/3) + (0 -

VDD) + (VDD/3 - 2VDD/3) + (VDD/3 - 2VDD/3) + (VDD/3 - 2VDD/3) + (VDD - 0) => VDC = 0

COM3 - SEG0 [OFF] = (2VDD/3 - VDD/3) + (2VDD/3 - VDD/3) + (2VDD/3 - VDD/3) + (0 - 0)

+ (VDD/3 - 2VDD/3) + (VDD/3 - 2VDD/3) + (VDD/3 - 2VDD/3) + (0 - 0) => VDC = 0

2.4

Octaplex LCD drive

In an octaplex LCD drive, eight backplanes are used. Each segment line is connected to

eight LCD segments, which other side is connected to one, two, four or eight of the eight

backplanes. Consequently, only (S/8)+8 MCU pins are necessary to drive an LCD with S

LCD segments. This mode is available only in medium+ and high density

STM8L152xx/STM8L162xx devices. For example, to drive an LCD with 320 LCD segments

(40 ×8), only 48 I/O ports are required (40 I/O ports to drive the segment lines and 8 I/O

ports to drive the backplanes).

V

ON RMS

()

VSi

()

2

n

∑

n

------------------------

3

VDD

3

-------------

⎝⎠

⎛⎞

2

VDD

()

2

3

VDD

–

3

----------------

⎝⎠

⎛⎞

2

VDD

–

()

2

++

+

8

----------------------------------------------------------------------------------------------------------------------

0,577VDD

==

=

V

OFF RMS

()

VSi

()

2

n

∑

n

------------------------

4

VDD

3

-------------

⎝⎠

⎛⎞

2

4

VDD

–

3

----------------

⎝⎠

⎛⎞

2

+

8

------------------------------------------------------------

0,333VDD

==

=

D

V

ON RMS

()

V

OFF RMS

()

-----------------------------

0,395

0,176

---------------

·

1,732

==

=