13-06-2012, 11:09 AM
Seminar on How to use the STM8L15x LCD controller
[attachment=24271]
Introduction
This application note describes techniques for connecting the STM8L15x LCD controller to
liquid crystal displays (LCD), for driving alphanumeric characters and converting ASCII
characters to LCD segment control codes.
It explains how to select the LCD glass well suited for your application, and how to configure
the LCD controller to take into account key parameters such as contrast, power
consumption, number of used pixels, operating frequency range, and blinking.
A brief description of the LCD segment drive firmware embedded on the STM8L1526-EVAL
evaluation board is also provided.
For more information on theSTM8L15x LCD controller, refer to the STM8L15x reference
manual (RM0031).
LCD solution
An LCD panel is composed of many layers. A liquid crystal is filled between two of them
(glass plates), that are separated by thin spacers coated with transparent electrodes which
contain orientation layers.
The orientation layer usually consists of a polymer (e.g. polyimide) which has been
unidirectionally rubbed using, for instance, a soft tissue. As a result, the liquid crystal
molecules are fixed with their alignment more or less parallel to the plates, in the direction of
rubbing. The crystal alignment directions at the surface of the two plates are perpendicular
so that the molecules between the two plates undergo a homogeneous twist deformation in
alignment to form a helix.
Selecting an LCD glass
To select the LCD glass best suited for your application among the wide range of products
available on the market, the following criteria must be taken into account:
1. The information to display on the LCD glass. It is a combination of alphanumeric
symbols and various useful predefined symbols such as digits, bells, low-battery
symbol, arrows, antenna, and progress bar.
2. The typical electrooptical characteristics required for the LCD to operate: operating
temperature, storage temperature, and operating voltage, which affect the LCD
contrast.
3. The number of pixels required to achieve the desired display on the LCD.
LCD controller drive signals
Single backplane LCD drive
In a single backplane drive, each LCD segment is connected to a segment line (Sx) and to a
backplane (common line) common to all the segments. A display using S segments is driven
with S+1 MCU output lines (S segments + 1common). The backplane is driven with a COM
signal between 0 and VDD with a duty cycle of 50%.
When switching on a segment, a signal with opposite polarity to COM is sent to the
corresponding Segment pin. When the non inverted COM signal is sent to the Segment pin,
the segment is off. Using an MCU, the I/O operates in output mode at either logic 0 or 1.
Duplex LCD drive
In a duplex drive, two backplanes are used instead of one. Each LCD segment line (Sx) is
connected to two LCD segments, which other side is connected to one of the two
backplanes or common lines (refer to Figure 4). Thus, only (S/2)+2 MCU pins are necessary
to drive an LCD with S segments.
[attachment=24271]
Introduction
This application note describes techniques for connecting the STM8L15x LCD controller to
liquid crystal displays (LCD), for driving alphanumeric characters and converting ASCII
characters to LCD segment control codes.
It explains how to select the LCD glass well suited for your application, and how to configure
the LCD controller to take into account key parameters such as contrast, power
consumption, number of used pixels, operating frequency range, and blinking.
A brief description of the LCD segment drive firmware embedded on the STM8L1526-EVAL
evaluation board is also provided.
For more information on theSTM8L15x LCD controller, refer to the STM8L15x reference
manual (RM0031).
LCD solution
An LCD panel is composed of many layers. A liquid crystal is filled between two of them
(glass plates), that are separated by thin spacers coated with transparent electrodes which
contain orientation layers.
The orientation layer usually consists of a polymer (e.g. polyimide) which has been
unidirectionally rubbed using, for instance, a soft tissue. As a result, the liquid crystal
molecules are fixed with their alignment more or less parallel to the plates, in the direction of
rubbing. The crystal alignment directions at the surface of the two plates are perpendicular
so that the molecules between the two plates undergo a homogeneous twist deformation in
alignment to form a helix.
Selecting an LCD glass
To select the LCD glass best suited for your application among the wide range of products
available on the market, the following criteria must be taken into account:
1. The information to display on the LCD glass. It is a combination of alphanumeric
symbols and various useful predefined symbols such as digits, bells, low-battery
symbol, arrows, antenna, and progress bar.
2. The typical electrooptical characteristics required for the LCD to operate: operating
temperature, storage temperature, and operating voltage, which affect the LCD
contrast.
3. The number of pixels required to achieve the desired display on the LCD.
LCD controller drive signals
Single backplane LCD drive
In a single backplane drive, each LCD segment is connected to a segment line (Sx) and to a
backplane (common line) common to all the segments. A display using S segments is driven
with S+1 MCU output lines (S segments + 1common). The backplane is driven with a COM
signal between 0 and VDD with a duty cycle of 50%.
When switching on a segment, a signal with opposite polarity to COM is sent to the
corresponding Segment pin. When the non inverted COM signal is sent to the Segment pin,
the segment is off. Using an MCU, the I/O operates in output mode at either logic 0 or 1.
Duplex LCD drive
In a duplex drive, two backplanes are used instead of one. Each LCD segment line (Sx) is
connected to two LCD segments, which other side is connected to one of the two
backplanes or common lines (refer to Figure 4). Thus, only (S/2)+2 MCU pins are necessary
to drive an LCD with S segments.