Driving LCD Displays Using XE8000 Standard I/O Ports

Application Note AN8000.13
Driving LCD Displays with I/Os
AN8000.13
Application Note
Driving LCD Displays using XE8000
standard I/O ports
Rev 1 February 2006
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1
Application Note AN8000.13
Driving LCD Displays with I/Os
Table of Contents
1
1.1
2
2.1
2.2
2.3
3
3.1
4
4.1
4.2
4.3
4.4
4.5
5
5.1
5.2
5.3
Introduction................................................................................................................................................. 3
Document structure .................................................................................................................................. 3
LCD Basics.................................................................................................................................................. 4
LCD direct drive........................................................................................................................................ 5
LCD multiplex drive .................................................................................................................................. 6
Mixing multiplex and direct drive .............................................................................................................. 7
Standard implementations ........................................................................................................................ 9
Driving a 4x8 segments LCD using standard microcontroller I/O ports................................................... 9
Application example................................................................................................................................. 10
Introduction............................................................................................................................................. 10
Hardware................................................................................................................................................ 10
Defining the LCD pins ............................................................................................................................ 10
Software – Constant & Variables ........................................................................................................... 11
Software - Functions .............................................................................................................................. 13
Annex A – Application source code ....................................................................................................... 16
Main file .................................................................................................................................................. 16
LCD Driver C file .................................................................................................................................... 17
LCD Driver Header file ........................................................................................................................... 22
© Semtech 2006
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2
Application Note AN8000.13
Driving LCD Displays with I/Os
1
INTRODUCTION
This application note intends to explain how to realize a simple LCD driver using the microcontrollers I/O ports.
The main goal of this document is to understand how to build a cheap LCD interface for small LCD displays for
example a STD 4.5 digit TN display.
1.1 DOCUMENT STRUCTURE
This document is separated in 5 sections
• Introduction: This section.
• LCD Basics: This section explains what is a LCD and different method to drive them.
• Standard implementations: This section explains how to implement the different driving methods
described in the chapter “LCD basics”.
• Application example: This section shows how to realize a LCD driver using an existing display.
• Application source code: Contains the source code of the application.
© Semtech 2006
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3
Application Note AN8000.13
Driving LCD Displays with I/Os
2
LCD BASICS
The Liquid Crystal Display (LCD) is a passive display technology. This means that this type of display does not
emit light; instead, it uses the ambient light from the environment. By manipulating this light, it displays images
using very little power. In addition LCDs can operate with relatively low voltage (2V and up). This has made LCDs
the preferred technology whenever low power consumption and compact size are critical.
LCDs are composed of two electrodes with liquid crystals placed between them. By applying a voltage to the
electrodes, the crystals change their orientation and modify the light polarization, which is revealed by a polarized
filter placed on the surface of the display.
electrode
electrode
liquid crystal
liquid crystal
electrode (backplane)
electrode (backplane)
AC voltage not applied, LC remains in its default
orientation, light goes through the filter.
AC voltage applied, LC changes its
orientation, light is blocked by the filter.
Liquid crystals are very sensitive to constant electric fields and DC voltages can cause an electrochemical reaction
which destroys the liquid crystals irreversibly, therefore only DC-free AC-voltages should be applied.
As soon as the amplitude of the applied AC field is superior to a given threshold (dependant upon the LCD
geometry and technology), the segment turns dark. If this amplitude is smaller than the same threshold, the
segment remains transparent. If the amplitude is very near to the threshold voltage, the segment remains gray or
glitches. Due to the specific characteristic described above, the way to drive a liquid crystal segment is as follows:
AC rms voltage
Crystal voltage
VDD
0V
VDD
VDD
or
Electrode 2
0V
VDD
VDD
0V
0V
VDD
crystal threshold
-VDD
0V
0V
Electrode 1
A) both signals in phase, the resulting voltage on the
crystal is 0V
VDD
Crystal voltage
Electrode 2
0V
AC rms voltage
VDD
VDD
0V
0V
VDD
-VDD
0V
crystal threshold
Electrode 1
B) both signals in counter-phase, the resulting voltage on
the crystal is +/- VDD
© Semtech 2006
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4
Application Note AN8000.13
Driving LCD Displays with I/Os
2.1 LCD DIRECT DRIVE
In multiple segments driving, one of the electrodes is common to all the segments, this electrode is called the
backplane (see drawing below). The backplane sends a square signal and the other electrodes send the same
signal with no phase shift for transparent segments or with a phase shift of 180° for dark segments.
VDD
Electrode 2 (segment 2)
Electrode 2
0V
VDD
Electrode 1
Electrode 1 (segment 1)
0V
VDD
Backplane (common)
0V
s1
s2
Backplane
Here segment 1 is “off” and
segment 2 is “on”
s1 voltage
AC
VDD
VDD
0V
0V
crystal threshold
-VDD
s2 voltage
AC rms voltage
VDD
VDD
0V
0V
-VDD
rms voltage
crystal threshold
The signal is in phase on segment s1 and in counter-phase on
segment s2, therefore the resulting voltage is 0 on segment s1 and
+/- VDD on segment s2
This way of driving LCD’s segments is the simplest one and the one that offers the best contrast, since the
resulting voltage on electrodes is VDD or 0V.
The drawback is that one needs one pin to drive each segment (plus one for the backplane), this may quickly lead
to huge numbers of connections to drive simple LCD displays.
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Application Note AN8000.13
Driving LCD Displays with I/Os
2.2 LCD MULTIPLEX DRIVE
In order to increase the number of segments one can increase the number of backplanes, this method enables one
electrode to drive more than one segment. In the example below each electrode drives two segments (Multiplex by
2). Segments must also have an “inactive” phase when their electrode carries the signal for the segments on the
other backplanes. This is done by adding intermediate signals onto each backplane. The AC voltage on one
segment is then integrated over a complete cycle through all the backplanes.
Electrode 2 (segment 3, 4)
VDD
Electrode 2
0V
Electrode 1 (segment 1, 2)
Electrode 1
VDD
0V
VDD
Backplane 1
s1
0V
VDD
s3
s4
Backplane 1
inactive
inactive
Backplane 2
s2
inactive
inactive
Backplane 2
0V
signal cycle
This way of driving introduces another parameter, now the resulting voltages between Electrodes and backplanes
are not 0V or VDD but values in between and the time to change all the segments is multiplied by the number of
backplanes.
If we do some calculations we can have the resulting voltage for each segment. See figure below.
Electrode 2
(segment 3, 4)
Electrode 1
(segment 1, 2)
VDD
Electrode 2
0V
VDD
Electrode 1
0V
VDD
s1
s2
s3
s4
Backplane 1
Backplane 2
Backplane 1
0V
VDD
Backplane 2
0V
s1: Electrode1 - Backplane1
-1
s2: Electrode1 - Backplane2
-0.5 0.5
1
0.5
-0.5
V11rms =
− 12 + 12 + 0.52 + −0.52
⋅ VDD = 0.791⋅ VDD
4
V12 rms =
− 0.52 + 0.52 + 02 + 02
⋅ VDD = 0.354 ⋅ VDD
4
V21rms =
0 2 + 0 2 + − 0 .5 2 + 0 .5 2
⋅ VDD = 0.354 ⋅ VDD
4
V22 rms =
0.52 + −0.52 + −12 + 12
⋅ VDD = 0.791⋅ VDD
4
s3: Electrode2 - Backplane1
-0.5 0.5
s4: Electrode2 - Backplane2
0.5 -0.5
Electrode Backplane
-1
1
Resulting signal
Mathematically we can see that Von (segment
visible) is situated at 0.791 x VDD and Voff
(segment invisible) is situated at 0.354 x VDD
Multiplying the backplanes allows one to address more segments, the drawback of this technique is that the delta
between Von and Voff is reduced; this implies that the contrast is also reduced.
LCD technology has fixed thresholds for Von and Voff, developers must take into account these thresholds and
ensure that generated Voff and Von must respect these thresholds.
The standard manner to increase contrast when using multiple backplanes is to generate 3 levels of voltage
instead of 2, but this technique is too complex to be implemented when using standard microcontroller I/O ports.
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6
Application Note AN8000.13
Driving LCD Displays with I/Os
2.3 MIXING MULTIPLEX AND DIRECT DRIVE
The main problem encountered using multiplex drive is that both “on” and “off” generated voltages may be above
or below the LCD thresholds. This is even more of an issue with bias ½ and high multiplexing ratios where “on” and
“off” generated voltages are not far from each other.
VDD
VDD
VDD
Ideal
Both under LCD “on”
threshold
Both above LCD “off”
threshold
Generated “on” rms voltage
Generated “off” rms voltage
LCD “on” threshold
LCD “off” threshold
As the direct drive does not have this limitation (full signal is applied to the segment or no signal is applied), a
simple way to shift the applied voltage is to mix multiplex and direct drive (see diagrams below). When using direct
drive for a short period of time, all backplanes are connected together to form a single backplane and a uniform
signal is applied to all electrodes, increasing or decreasing the mean RMS voltage applied to the whole LCD. By
changing the ratio between the uniform direct drive signal and the addressed multiplexed signal, one moves the
mean applied “on” and “off” levels.
Shifting Down Generated Thresholds
Electrode 2
(segment 3, 4)
Electrode 1
(segment 1, 2)
Backplane 1
Backplane 2
VDD
Electrode 2
0V
VDD
Electrode 1
0V
VDD
0V
VDD
s1
s2
s3
s4
Backplane 1
Backplane 2
0V
0.8 0.8
Segment1 vs Backplane1
Segment2 vs Backplane2
0.4
0.4
Two signals
superposition
Resulting signal
0.4
Von =
0.82 + 0.82 + 0.4 2 + 0.4 2
⋅ VDD = 0.633 ⋅ VDD
4
0
Voff =
0 2 + 0 2 + 0.4 2 + 0.4 2
⋅ VDD = 0.283 ⋅ VDD
4
0.4
0
Mathematically we can see that Von (segment visible) is
situated at 0.633 x VDD and Voff (segment invisible) is
situated at 0.283 x VDD
As shown in figures above, direct drive waveforms are forced during a short period of time at the beginning of each
pulse forcing them to 0V will shift down the average resulting values of generated thresholds and vice-versa.
© Semtech 2006
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7
Application Note AN8000.13
Driving LCD Displays with I/Os
Shifting Up Generated Thresholds
Electrode 2
(segment 3, 4)
Electrode 1
(segment 1, 2)
Backplane 1
Electrode 2
VDD
0V
VDD
Electrode 1
0V
VDD
0V
VDD
Backplane 2
s1
s2
s3
s4
Backplane 1
Backplane 2
0V
1
Segment1 vs Backplane1
1
0.6
Segment2 vs Backplane2
0.6
Two signals
superposition
Resulting signal
© Semtech 2006
0.6
0.6
Von =
0.2 0.2
Voff =
12 + 12 + 0.6 2 + 0.6 2
⋅ VDD = 0.825 ⋅ VDD
4
0.2 2 + 0.2 2 + 0.6 2 + 0.6 2
⋅ VDD = 0.447 ⋅ VDD
4
Mathematically we can see that Von (segment visible) is
situated at 0.825 x VDD and Voff (segment invisible) is
situated at 0.447 x VDD
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Application Note AN8000.13
Driving LCD Displays with I/Os
3
STANDARD IMPLEMENTATIONS
When using multiple backplanes, the signal on the backplanes becomes analog; this means when using
microcontroller’s standard I/O ports that external circuitry must be added in order to produce this analog waveform.
Following are examples on how to set up the circuitry in order to obtain multiplex by two waveforms.
Microcontroller
t0 t1 t2 t3
States to generate waveforms
a
µC
a
a
1
0
HiZ
HiZ
b
b
b
HiZ
HiZ
1
0
a
1
0
0.5
0.5
b
0.5
0.5
1
0
a1
a0
b1
b0
The figure above shows the most common way to create the analog waveforms playing with the High impedance
capability of the I/O ports
Microcontroller
t0 t1 t2 t3
ab1
ab
ab0
a
µC
b
BCD codes to generate waveforms
a
1
0
0
1
bc1
bc
bc0
c
b
1
0
1
0
c
0
1
1
0
ab
1
0
0.5
0.5
bc
0.5
0.5
1
0
ab1
ab0
bc1
bc0
The figure above shows an alternative for I/O ports that do not have the High impedance capability.
Note that putting the I/O port as an input cannot be considered as a true HiZ, and in this case can lead to uncertain
behavior since value of the input voltage is VDD/2.
3.1 DRIVING A 4X8 SEGMENTS LCD USING STANDARD MICROCONTROLLER I/O PORTS
Application schematic
Microcontroller
t0
a
ab
b
bc
c
µC
d
L7
L6
L5
L4
L3
L1
L0
e
t2 t3 t4 t5 t6 t7
LCD 4x8
ab0
bc1
bc0
cd
L2
t1
ab1
de
cd1
cd0
de1
de0
L0
L1
L2
L3
L4
L5
L6
L7
© Semtech 2006
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Application Note AN8000.13
Driving LCD Displays with I/Os
4
APPLICATION EXAMPLE
4.1 INTRODUCTION
In this chapter we will setup an example application using an LCD, based on the theory of the previous chapters.
The goal is to be able to develop an LCD driver with any simple LCD display.
Knowing the pin assignment of the LCD will allow you to develop the corresponding driver.
4.2
HARDWARE
1 XE8000MP
1 XE8000EV101
1 Display LCD DISPLAYTECH 066-P2 MUX3 36 seg
4.2.1
LCD Hardware
The LCD hardware is described below:
Pin mapping:
1
1F
2
1A
3
1B
4
2F
5
2A
6
2B
3F
7
8
3A
3B
9
10
4F
11
4A
12
4B
1E
1G
1C
2E
2G
2C
3E
3G
3C
4E
4G
4C
DP1
1D
K
DP2
2D
-
DP3
3D
LOBAT
DP4
4D
CONT
13
COM1
14
15
16-30
NC
COM2
COM3
4.3 DEFINING THE LCD PINS
If we want to drive all the segments we have to use PC0 to PC7 and PB0 to PB3 for the signal driving and PB5 to
PB7 to generate the common waveforms.
In this case, pins have been assigned as follows:
ports
LCD
pins
com1
PC
0
PC
1
1
2
PC
2
3
PC
3
PC
4
PC
5
PC
6
PC
7
PB
0
PB
1
PB
2
4
5
6
7
8
9
10
11
PB
3
12
1F
1A
1B
2F
2A
2B
3F
3A
3B
4F
4A
4B
1E
1G
1C
2E
2G
2C
3E
3G
3C
LO
BAT
4E
4G
4C
com2
com3
DP1
1D
K
DP2
2D
-
DP3
3D
© Semtech 2006
DP4
4D
CONT
PB
6-7
13
COM
1
PB
6-5
14
PB
5-7
15
COM
2
1630
NC
COM
3
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Application Note AN8000.13
Driving LCD Displays with I/Os
4.3.1
Choosing The Common Waveform Generation Schematic
Since the XE8801A can only use analog mode (equivalent to Hi-Z) when using pairs of pins, the alternative
chained resistor schematic as shown in standard implementations, has to be used. The chained resistor schematic
is more complex to implement but allows the use of single pins rather than pairs, without using the analog mode
4.3.2
Application Schematic
Microcontroller
R = 6 x 330K
t0
ca
ab
PB5 a
PB6 b
XE8801A
t1
t2
t3
t4
t5
COM1
ca1
ca0
ab1
COM2
bc
ab0
PB7 c
bc1
PC0 - PB3
L0 – L11
COM3
bc0
12
Lx
12
4.4 SOFTWARE – CONSTANT & VARIABLES
Definitions of constants and variables
4.4.1
LCD Com Constant Table
In order to generate the common wave forms we have to define an array containing six constants corresponding to
the six possible states on the common lines: AB1, AB0, BC1, BC0, CA1 and CA0.
a
1
0
1
0
0
b
0
1
1
0
1
c
1
0
0
1
1
ab
0.5
0.5
1
0
0.5
bc
0.5
0.5
0.5
0.5
1
ca
1
0
0.5
0.5
0.5
ca1
ca0
ab1
ab0
bc1
PB7
1
0
0
1
1
PB6
0
1
1
0
1
PB5
1
0
1
0
0
PB4
0
0
0
0
0
PB3
0
0
0
0
0
PB2
0
0
0
0
0
PB1
0
0
0
0
0
PB0
0
0
0
0
0
hex
0xA0
0x40
0x60
0x80
0xC0
1
0
0
0.5
0
0.5
bc0
0
0
1
0
0
0
0
0
0x20
4.4.2
LCD Data Constant Table
To display numbers we need to have another constant table that contains the seven segments states for each
number.
a
0
1
2
3
4
5
6
7
8
9
1
0
1
1
0
1
1
1
1
1
b
1
1
1
1
1
0
0
1
1
1
c
1
1
0
1
1
1
1
1
1
1
d
1
0
1
1
0
1
1
0
1
0
e
f
1
0
1
0
0
0
1
0
1
0
1
0
0
0
1
1
1
0
1
1
g
0
0
1
1
1
1
1
0
1
1
hex
0x7E
0x30
0x6D
0x79
0x33
0x5B
0x5F
0x70
0x7F
0x73
F
B
E
B
C
C
D
A
F
A
A
A
G
C
C
D
D
© Semtech 2006
E
B
G
C
C
D
A
B
G
E
F
B
G
D
A
A
F
B
G
C
F
G
E
A
B
F
G
C
C
D
B
D
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Application Note AN8000.13
Driving LCD Displays with I/Os
4.4.3
LCD Lines Variable Table
This variable is a picture of the display and is used to refresh the LCD; one must modify this table in order to see
the display changing at the next refresh.
This variable is the most important. It represents the actual LCD display state.
The table below represents the variable organization; we can see that every segment is represented for each
phase of the LCD frame. (Note that “!” represent the Boolean operation NOT)
13
14
15
1
2
3
4
5
6
7
8
9
10
11
12
PC0
PC1
PC2
PC3
PC4
PC5
PC6
PC7
PB0
PB1
PB2
PB3
c1+
c1c2+
c2c3+
!1f
1f
!1e
1e
!DP1
!1a
1a
!1g
1g
!1d
!1b
1b
!1c
1c
!K
!2f
2f
!2e
2e
!DP2
!2a
2a
!2g
2g
!2d
!2b
2b
!2c
2c
!-
!3f
3f
!3e
3e
!DP3
!3a
3a
!3g
3g
!3d
!3b
3b
!3c
3c
!LOBAT
!4f
4f
!4e
4e
!DP4
!4a
4a
!4g
4g
!4d
!4b
4b
!4c
4c
!CONT
c3-
DP1
1d
K
DP2
2d
-
DP3
3d
LOBAT
DP4
4d
CONT
Note: This table is initialized with all segments “off”.
© Semtech 2006
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Application Note AN8000.13
Driving LCD Displays with I/Os
4.5
SOFTWARE - FUNCTIONS
4.5.1 Refresh Line
In order to display a value on the LCD we must implement a function that will modify the LCD_Lines[ ] variable.
This function will use LCD_Data[ ] constants as a template to set the wanted segments of the wanted digit.
The special symbols such as DPx, LOBAT or CONT will be managed through another function described later in
this document.
We will call this function Refresh_Line. This function will have 2 arguments. The first argument will be used as an
index to the LCD_Data[ ] constant table (Digits template). The second argument corresponds to the digit to be
displayed.
In order to simplify the code, the LCD_Data[ ] table has been rearranged in order to fit the LCD display physical
layout.
The two tables below gives a representation of the Refresh_Line function behavior.
LCD_Data[ ]
c
b
d
g
a
e
f
hex
function call : Refresh_Line ( 9, 4 )
0
1
1
1
0
1
1
1
0x77
1
1
1
0
0
0
0
0
0x03
2
0
1
1
1
1
1
0
0x5D
3
1
1
1
1
1
0
0
0x1F
4
1
1
0
1
0
0
1
0x2B
5
1
0
1
1
1
0
1
0x3E
6
1
0
1
1
1
1
1
0x7E
7
1
1
0
0
1
0
0
0x07
8
1
1
1
1
1
1
1
0x7F
9
1
1
0
1
1
0
1
0x2F
7
6
5
4
3
2
1
1. The function takes the number 9, segment f
value in the table LCD _Data [ ]
2. This value is inverted and placed at the fourth
digit to enable the f segment (c1+ !4F)
3. Then the non inverted value is placed at the
fourth digit to enable the f segment (c1- 4F)
4. Points 1 to 3 are repeated for all the
segments of the fourth digit
1
LCD_Lines[ ]
12
11
10
9
8
7
6
5
4
3
2
1
PB2
0 !4a
PC7
PC6
PC5
PC4
PC3
PC2
PC1
PC0
!3b
!3a
!3f
!2b
!2a
!2f
!1b
!1a
!1f
1 4a
PB1
0 !4f 2
1
1 4f 3
PB0
c1-
PB3
0 !4b
1 4b
3b
3a
3f
2b
2a
2f
1b
1a
1f
c2+
1 !4c
0 !4g
0 !4e
!3c
!3g
!3e
!2c
!2g
!2e
!1c
!1g
!1e
c2-
0 4c
c3+
!CONT
1 4g
1 !4d
c3-
CONT
0 4d
c1+
6
7
3
4
1 4e
5
2
3c
3g
3e
2c
2g
2e
1c
1g
1e
!DP4
!LOBAT
!3d
!DP3
!-
!2d
!DP2
!K
!1d
!DP1
DP4
LOBAT
3d
DP3
-
2d
DP2
K
1d
DP1
© Semtech 2006
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13
Application Note AN8000.13
Driving LCD Displays with I/Os
4.5.2 Set Special
As special symbols can be considered as flags on the LCD display, this function allows all of them to be set
individually.
We will call this function SetSpecial. This function will have 2 arguments. The first argument will be a predefined
value corresponding to the symbol to be displayed (DPx, LOBAT…) . The second argument corresponds to the
state of the symbol (0 = OFF, 1 = ON)
The table below gives a representation of the SetSpecial function behavior.
Function call: SetSpecial( DP1, 1 )
1
Place a 0 at the symbol DP1 (c3+ !DP)
2
Place a 1 at the symbol DP1 (c3- DP)
LCD_Lines[ ]
c1+
12
11
10
9
8
7
6
5
4
3
2
1
PB3
PB2
PB1
PB0
PC7
PC6
PC5
PC4
PC3
PC2
PC1
PC0
!4b
!4a
!4f
!3b
!3a
!3f
!2b
!2a
!2f
!1b
!1a
!1f
c1-
4b
4a
4f
3b
3a
3f
2b
2a
2f
1b
1a
1f
c2+
!4c
!4g
!4e
!3c
!3g
!3e
!2c
!2g
!2e
!1c
!1g
!1e
c2-
4c
4g
4e
3c
3g
3e
2c
2g
2e
1c
1g
c3+
!CONT
!4d
!DP4
!LOBAT
!3d
!DP3
!-
!2d
!DP2
!K
!1d
0 !DP1
1d
1 DP1 2
c3-
4.5.3
CONT
4d
DP4
LOBAT
3d
DP3
-
2d
DP2
K
1e
1
LCD Refresh
In order to avoid the LCD display blinking the index of the LCD_Lines[x] array must be changed at least 150 times
per second. This means a complete display refresh every 25 times per second (25Hz) which is the physical limit for
the eye to not see the refresh.
Moreover, to implement the contrast correction as described in the chapter “Mixing multiplex and direct drive” we
need to have a faster refresh rate, see the timing diagrams below.
Contrast correction scheme
Std Multiplex scheme
40 ms max (25Hz)
40 ms max (25Hz)
t0 t5 t10 t15 t20 t25 t30
t0 t1 t2 t3 t4 t5
c1+
c1+
COM1
c1-
COM1
c1-
c2+
c2+
COM2
c2c3+
COM2
c2c3+
COM3
c3-
Lx
LCD
Lines
COM3
c3-
Lx
LCD Lines
t0 = 6.7ms
t0 = 1.3ms
In this example we choose to have 6 steps to correct the contrasts, this implies a higher refresh frequency.
© Semtech 2006
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14
Application Note AN8000.13
Driving LCD Displays with I/Os
The function will be called LCDRefresh and will have to be called at least every 1.3 ms. This function does not
need any arguments.
This function uses a variable that contains a set of flags, these flags will be used to generate the correct pulse
widths for the contrast correction and the data display.
The diagram below shows the timings generated through these flags.
LCDFlags
ratio
AB = 0
1
pulse
AB = 0.5
1
polarity
AB = 1
1
correction
9
1
Not used
10
5
x
Not used
6
1
x
ratio:
Triggers the writing of the contrast correction pulse
pulse:
Triggers the writing of the standard multiplex pulse
polarity:
Determines the current polarity of the common.
Correction:
Inverts the correction shift if at 1.
ratio
2
x
Not used
pulse
x
Not used
polarity
AB = 0.5
AB = 0.5
3
7
11
4
8
12
AB = 0.5
Contrast correction pulse, depends
on polarity, ratio & correction flags
Standard multiplex drive, depends
on pulse flags
The table below shows the different states of the flags
state
0
1
2
3
4
5
6
7
8
9
10
11
12
rat
0
0
1
0
1
0
1
0
1
0
1
0
1
pul
0
0
0
1/0
0
1/0
0
1/0
0
1/0
0
1/0
0
pol
1
1
1
0
0
1
1
0
0
1
1
0
0
cor
0
0
0
0
0
0
0
0
0
0
0
0
0
AB =
1
LCD_COM[0]
0
LCD_COM[1]
1
LCD_COM[2]
0
LCD_COM[3]
1
LCD_COM[4]
0
LCD_COM[5]
© Semtech 2006
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15
Application Note AN8000.13
Driving LCD Displays with I/Os
5
ANNEX A – APPLICATION SOURCE CODE
This LCD driver can be found annexed in a zip file, some other functions have been added in order to simplify the
use of the LCD display.
Functions added:
void Number2LCD (_U16 Value);
void InitLCD(void);
void AllChar(_U8 State);
void LCDOff(void);
This function takes a number from 0 to 9999 and displays it on the LCD
This function inits the hardware (counters ports etc..)
This function clears/displays all the segments of the LCD
This function clears the LCD and disables all the peripherals
In the zip file you will find two projects, one is the standard template including the LCD driver below; the other is a
basic clock application.
Below is the main file of the standard template showing the minimum code to write to see something on the LCD.
5.1
MAIN FILE
/*******************************************************************
** File
: main.c
**
********************************************************************
**
**
** Version
:
**
**
**
** Writen by
:
**
**
**
** Date
: XX-XX-XXXX
**
**
**
** Project
: **
**
**
********************************************************************
** Changes
:
**
********************************************************************
** Description : Main program
**
*******************************************************************/
#include "Globals.h"
/*******************************************************************
** Global variables declaration
**
*******************************************************************/
_U8 Toggle = TRUE;
// Global variable changed in irq 128Hz
/*******************************************************************
** main : Main program function
**
********************************************************************
** In
: **
** Out : **
*******************************************************************/
int main (void){
_U16 i;
InitMicro();
_Monitor_Init();
_Monitor_SoftBreak;
InitLCD();
// Initializes the microcontroller (RC @ 1MHz)
// Initializes LCD
RegIrqEnHig |= 0x40;
// Enables the 128Hz interrupt
while(1){
//displays numbers from 0 to 9999
for (i = 0 ; 9999 > i; i++){
Number2LCD (i);
// display the current loop value
do{
asm("halt");// waits for the 1Hz interrupt
}while(!Toggle);
Toggle = FALSE;
}
}
return 0;
}
void Handle_Irq_128Hz (void){
Toggle = TRUE;
}
© Semtech 2006
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16
Application Note AN8000.13
Driving LCD Displays with I/Os
5.2
LCD DRIVER C FILE
/*******************************************************************
** File
: 0x_LcdDriver.c
**
********************************************************************
**
**
** Version
: V 1.0
**
**
**
** Writen by
: Gregoire Guye
**
**
**
** Date
: 21-02-2005
**
**
**
** Project
: **
**
**
********************************************************************
** Changes
:
**
********************************************************************
** Description : 0x LCD driver
**
*******************************************************************/
#include "0x_LcdDriver.h"
/*******************************************************************
** Global variables declaration
**
*******************************************************************/
// Common Scheme
_U8 LCD_Com[] = {CA1, CA0, AB1, AB0, BC1, BC0};
// Display Scheme initialized at LCD off (all 0)
_U16 LCD_Lines[]
= {0xFFFF, 0x0000, 0xFFFF, 0x0000, 0xFFFF, 0x0000 };
// Ports image
// Numbers from 0 to null predefined
//
0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17
// data (0,1,2,3,4,5,6,7,8,9,- , ,c ,l ,e ,t ,b ,n)
_U8 LCD_Data[] = {0x77,0x60,0x3E,0x7C,0x69,0x5D,0x5F,0x64,0x7F,0x6D,0x08,0x00,0x17,
0x13,0x1F,0x1B,0x5B,0x4A};
volatile _U8 CountInt,CountIntStep = 1;
_U8 LCDFlags = 0x08;
_U8 CountIntTick;
_U8 CurrentLine = 0x00;
© Semtech 2006
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17
Application Note AN8000.13
Driving LCD Displays with I/Os
/***************************************************************************
** Refresh_Line : Transposes a number in a digit
**
****************************************************************************
** This routines transposes the values stored in the LCD_Datatable to the **
** table used to display values on LCD , in this case a 6 rows x 12 col
**
** disposed as follow :
**
**
**
**
LCD_Lines[]
**
**
/-------------------------------------------------------------\
**
**
|PB3 .PB2|PB1 . PB0 |PC7 . PC6|PC5 . PC4|PC3 . PC2|PC1 . PC0|
**
** c1+|!4B .!4A|!4F .!3B
|!3A .!3F |!2B .!2A |!2F .!1B|!1A .!1F |
**
** c1-| 4B . 4A| 4F . 3B
| 3A . 3F | 2B . 2A | 2F . 1B| 1A . 1F |
**
** c2+|!4C .!4G|!4E .!3C
|!3G .!3E |!2C .!2G |!2E .!1C|!1G .!1E |
**
** c2-| 4C . 4G| 4E . 3C
| 3G . 3E | 2C . 2G | 2E . 1C| 1G . 1E |
**
** c3+|!CONT.!4D|!DP4.!LOBAT|!3D .!DP3|!- .!2D |!DP2 .!K |!1D .!DP1|
**
** c3-| CONT. 4D| DP4. LOBAT| 3D . DP3| - . 2D | DP2 . K | 1D . DP1|
**
**
+-----+---+----+------+----+----+----+----+-----+---+----+----+
**
**
**
****************************************************************************
** In
: number (0-null), digit_no (0-3)
**
** Out
: - (LCD_lines modified)
**
***************************************************************************/
void Refresh_Line (_U8 number, _U8 digit_no ){
_U8 i, Lines_index, phase;
_U16 mask, temp ,curr_num;
Lines_index = 0;
// initializes the line index
phase = 0;
// with phase = 0 first "1" on commons
digit_no = (3 - digit_no);
digit_no *= 3;
// Transforms digit_no to column index (3 multiple)
mask = 0x01;
// Initialises the mask
mask <<= digit_no;
// Place it to the right column
curr_num = LCD_Data[number];
// Copy the Sline corresponding number
for (i = 0; i < 14; i++){
phase ^= 0x01;
// Toggles the phase
if(phase){
// Write the current val & its inverse successively
temp = (~curr_num & 0x01);
// Mask the current val (inverse) and save it in temp
}else{
temp = (curr_num & 0x01);
// Mask the current val and save it in temp
curr_num >>= 1;
// Seek the next current val to write
}
temp <<= digit_no;
// Places the value to its correct digit place
LCD_Lines[Lines_index] &= ~mask;
// Clears the previous value then write the new value
LCD_Lines[Lines_index] |= (temp & mask);
Lines_index++;
// Writes next line
if (i == 3){
// If the number of lines max -1 is reached
mask <<= 1;
// Moves the mask by 1
digit_no++;
// Changes the line to write
Lines_index = 0;
// Re-initializes the line index
}else if (i == 9){
mask <<= 1;
// Moves the mask by 1
digit_no++;
// Changes the line to write
Lines_index = 0;
// Re-initializes the line index
}
}
}
© Semtech 2006
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18
Application Note AN8000.13
Driving LCD Displays with I/Os
/*******************************************************************
** Display_LCD : Displays the current value of LCD_line table
**
********************************************************************
** In : **
** Out : **
*******************************************************************/
void Display_LCD (void){
_U8 IntPBVal, IntPCVal;
if (CountIntTick == CountIntStep){
LCDFlags |= 0x01;
// Sets Ratio Flag to 1
}
else if (CountIntTick == 6){
LCDFlags |= 0x03;
// Sets Pulse &Ratio flags to 1
CountIntTick = 0;
}
if(CountIntTick == 0 && ((LCDFlags & 0x03) == 0x03)){
}else{
CountIntTick++;
}
// Standard MUX3 drive section
if((LCDFlags & 0x01) == 0x01){
if((LCDFlags & 0x02) == 0x02){
LCDFlags ^= 0x04;
// toggles the polarity flag
LCDFlags &= ~0x03;
// Clears the Ratio & Pulses flags
CurrentLine++;
}else{
// Save the current ports values
IntPBVal = RegPBOut;
IntPCVal = RegPCOut;
// Clears the correct pins according to predefined masks
IntPBVal &= ~(COMMON_MASK3 | LINE_MASK2);
IntPCVal &= ~LINE_MASK1;
// Applies the common pattern
IntPBVal |= (LCD_Com[CurrentLine]& COMMON_MASK3);
// Applies the data patterns
IntPCVal |= (LCD_Lines[CurrentLine] & LINE_MASK1);
IntPBVal |= ((LCD_Lines[CurrentLine] >> 8) & LINE_MASK2);
// Update the display
RegPBOut = IntPBVal;
RegPCOut = IntPCVal;
}
}
// End of Standard MUX3 drive section
// Contrast adjustment section
else{
// Force the Commons to 0 or 1 during the period defined by the ratio
if((LCDFlags & 0x04) == 0x04){
RegPBOut |= COMMON_MASK3;
// Forces Commons to 1
}else{
RegPBOut &= ~COMMON_MASK3;
// Forces Commons to 0
}
// Force the Data to 0 or 1 during
if((LCDFlags & 0x04) == ((LCDFlags
RegPCOut |= LINE_MASK1;
RegPBOut |= LINE_MASK2;
}else{
RegPCOut &= ~LINE_MASK1;
RegPBOut &= ~LINE_MASK2;
}
}
// End of Contrast adjustment section
if(CurrentLine == 6){
CurrentLine = 0;
}
the period defined by the ratio
& 0x08)>> 1)){
// Forces Datas to 1 (PC0 - PC7)
// Forces Data to 1 (PB0 - PB3)
// Forces Datas to 0 (PC0 - PC7)
// Forces Data to 0 (PB0 - PB3)
// End of the table = 6
}
© Semtech 2006
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19
Application Note AN8000.13
Driving LCD Displays with I/Os
/*******************************************************************
** SetSpecial : Sets the Special characters on LCD_Lines
**
********************************************************************
** In
: Special char to modify DP1, K, DP2, MINUS,
**
**
DP3, LOBAT, DP4, CONT
**
**
State 0 / 1
**
** Out
: **
*******************************************************************/
void SetSpecial(_U8 Schar, _U8 State){
_U16 mask = 0x01;
mask <<= (Schar);
// Shift the mask at the correct column
if (State){
LCD_Lines[4]&= ~mask;
// Unsets the corresponding bit
LCD_Lines[5]|= mask;
// Set the corresponding bit (inverse)
}else{
LCD_Lines[4]|= mask;
// Sets the corresponding bit
LCD_Lines[5]&= ~mask;
// Unsets the corresponding bit (inverse)
}
}
/*******************************************************************
** AllChar : Sets all the Characters on LCD_Lines
**
********************************************************************
** In
: State 0 / 1
**
** Out
: **
*******************************************************************/
void AllChar(_U8 State){
if (State){
LCD_Lines[0] &= ~0x7FFF;
LCD_Lines[1] |= 0x7FFF;
LCD_Lines[2] &= ~0x7FFF;
LCD_Lines[3] |= 0x7FFF;
LCD_Lines[4] &= ~0x7FFF;
LCD_Lines[5] |= 0x7FFF;
}
else{
LCD_Lines[0] |= 0x7FFF;
LCD_Lines[1] &= ~0x7FFF;
LCD_Lines[2] |= 0x7FFF;
LCD_Lines[3] &= ~0x7FFF;
LCD_Lines[4] |= 0x7FFF;
LCD_Lines[5] &= ~0x7FFF;
}
}
/*******************************************************************
** Number2LCD : Transposes a 3 digits number on the LCD display
**
********************************************************************
** In : Value (0-9999)
**
** Out : **
*******************************************************************/
void Number2LCD (_U16 Value){
Refresh_SLine
Refresh_SLine
Refresh_SLine
Refresh_SLine
((Value % 10), 0);
(((Value / 10) % 10), 1);
(((Value / 100) % 10), 2);
(((Value / 1000) % 10), 3);
}
/*******************************************************************
** InitLCD : Initialises the counters for the LCD
**
********************************************************************
** In
: **
** Out
: **
*******************************************************************/
void InitLCD(void){
RegPCOut
RegPCDir
RegPBDir
RegPBOpen
RegPBPullup
RegCntCtrlCk
RegCntConfig1
RegCntC
RegIrqEnHig
RegCntOn
= 0x00;
= 0xFF;
= 0xFF;
= 0x00;
= 0xFF;
|= 0x10;
&= ~0x40;
= 0x18;
|= 0x08;
|= 0x04;
//
//
//
//
//
//
//
//
//
//
Set PC out at 0
Sets PortC pins as outputs
Sets PortB pins as outputs
Port B hasn't open drain outputs
No Pullups
ck for counter C = 32KHz
Counter C down counting
1.3kHz
Authorize interrupt Counter C (240Hz)
Starts the counter C
}
© Semtech 2006
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20
Application Note AN8000.13
Driving LCD Displays with I/Os
/*******************************************************************
** LCDOff : Switches off the LCD Display
**
********************************************************************
** In
: **
** Out
: **
*******************************************************************/
void LCDOff(void){
AllChar(0);
// Clears the LCD display
RegPCOut
= 0x00; // Clears PortC
RegPBOut
&= ~0xEF; // Clears PortB
RegIrqEnHig
&= ~0x08; // Disable interrupt Counter C (240Hz)
RegCntOn
&= ~0x04; // Stops the counter C
}
/*******************************************************************
** Interrupts Handling
**
*******************************************************************/
/*******************************************************************
** Handle_Irq_CntC : Handles the interruption Counter C that
**
**
clocks the LCD display in order to have a
**
**
total frame of 32Hz
**
********************************************************************
** In
: **
** Out
: **
*******************************************************************/
void Handle_Irq_CntC (void){
Display_LCD ();
} //End Handle_Irq_CntC
© Semtech 2006
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21
Application Note AN8000.13
Driving LCD Displays with I/Os
5.3
LCD DRIVER HEADER FILE
/*******************************************************************
** File
: 0x_LcdDriver.h
**
********************************************************************
**
**
** Version
: V 1.0
**
**
**
** Writen by
: Gregoire Guye
**
**
**
** Date
: 21-02-2005
**
**
**
** Project
: **
**
**
********************************************************************
** Changes
:
**
********************************************************************
** Description : 0x LCD driver
**
*******************************************************************/
#ifndef __0X_LCDDRIVER__
#define __0X_LCDDRIVER__
/*******************************************************************
** Include files
**
*******************************************************************/
#include "Globals.h"
/*******************************************************************
** Global definitions
**
*******************************************************************/
// Commons waveforms
// +_---- F ---+_
#define AB1 0x60 // | | _______| | ____________
#define AB0 0x80 //
|_|_
¦ |_|_
#define BC1 0xC0 // ____| | ___¦____| | ________
#define BC0 0x20 //
|_|_ ¦
|_|_
#define CA1 0xA0 // ________| | ¦________| | ____
#define CA0 0x40 //
|_|_
|_|
// Digits
#define
#define
#define
#define
D1
D2
D3
D4
3
2
1
0
//
//
//
//
Digit1
Digit2
Digit3
Digit4
Xxxx
xXxx
xxXx
xxxX
// Special Chars
#define
#define
#define
#define
#define
#define
#define
#define
DP1
K
DP2
MINUS
DP3
LOBAT
DP4
CONT
0
2
3
5
6
8
9
11
//
//
//
//
//
//
//
//
Decimal point 1
"1" Icon
Decimal point 2
"-" Icon
Decimal point 3
low bat Icon
Decimal point 4
Continuity Icon
// Masks
#define COMMON_MASK3 0xE0
#define LINE_MASK1
#define LINE_MASK2
0xFF
0x0F
// (PB5 to PB7) Mux 3
// (PC0 to PC7)
// (PB0 to PB3)
// Special
#define
#define
#define
#define
#define
#define
#define
#define
_MINUS 10
_NULL 11
_C 12
_L 13
_E 14
_T 15
_B 16
_N 17
© Semtech 2006
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22
Application Note AN8000.13
Driving LCD Displays with I/Os
© Semtech 2006
All rights reserved. Reproduction in whole or in part is prohibited without the prior written consent of the copyright owner. The
information presented in this document does not form part of any quotation or contract, is believed to be accurate and reliable and
may be changed without notice. No liability will be accepted by the publisher for any consequence of its use. Publication thereof
does not convey nor imply any license under patent or other industrial or intellectual property rights. Semtech. assumes no
responsibility or liability whatsoever for any failure or unexpected operation resulting from misuse, neglect improper installation,
repair or improper handling or unusual physical or electrical stress including, but not limited to, exposure to parameters beyond the
specified maximum ratings or operation outside the specified range.
SEMTECH PRODUCTS ARE NOT DESIGNED, INTENDED, AUTHORIZED OR WARRANTED TO BE SUITABLE FOR USE IN
LIFE-SUPPORT APPLICATIONS, DEVICES OR SYSTEMS OR OTHER CRITICAL APPLICATIONS. INCLUSION OF SEMTECH
PRODUCTS IN SUCH APPLICATIONS IS UNDERSTOOD TO BE UNDERTAKEN SOLELY AT THE CUSTOMER’S OWN RISK.
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hold Semtech and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs damages and
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Contact Information
Semtech Corporation
Wireless and Sensing Products Division
200 Flynn Road, Camarillo, CA 93012
Phone (805) 498-2111 Fax : (805) 498-3804
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