Serial Communication with LC Controllers and Displays
A 485 Project By:
Paul J. Lansing
Jason A. Ahrendt
Jason D. Marsack
Presented to:
Rabinyara Mahapatara
In Fulfillment of the Requirements for CPSC 485
Summer 1998
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Serial to Parallel
Communication
I GOT THE BUS
I GOT THE BUS
I GOT THE BUS
I GOT THE BUS
Table of Contents
1.
SERIAL BUFFER
1.1 RS232 and Serial Communications
1.2 Max232 Line Driver
1.3 6850 Asynchronous Communications Interface Adapter
1.4 Xilinx Control Module
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2
3
4
5
2.
TEXT LIQUID CRYSTAL DISPLAY AND CONTROLLER
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3. LM211 Graphical LCD DISPLAY AND CONTROLLER
3.1 Introduction to the LM211
3.2 Physical Construction
3.3 Voltage Source Requirements
3.4 Control Signal Requirements
3.5 LM211DVR Xilinx Control Module
3.6 Protocol for the LM211DVR
3.7 Sub-Modules of the LM211DVR
7
4. Aggregation of Separate Components
14
5. Appendix A: Figures for Serial Buffer
Figure 1.1 Serial Buffer Test fixture
Figure 1.2 Serial Buffer Sub-Module
Figure 1.3 Control Module State Diagram
Figure 1.4 Control Module ABEL Code
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6. Appendix B: Figures for Text LCD Display and Controller
Figure 2.1
Figure 2.2
Figure 2.3
Figure 2.4
Figure 2.5
Figure 2.6
Figure 2.7
Figure 2.8
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7. Appendix C: Figures for Graphical LCD Display and Controller
Figure 3.1
Figure 3.2
Figure 3.3
Figure 3.4
Figure 3.5
Figure 3.6
Figure 3.7
Figure 3.8
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8. Appendix D: Hitachi LM211 Data Sheet
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9. Appendix E: Shift Register Data Sheets
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3.1 Introduction to the LM211 LCD Display
The LM211 is a Hitachi product. It was first used in the early eighties in medical devices
and has since then been phased out of use almost completely (Only a few CS students at
Texas A&M University still use this panel). This may discourage a user at first, but the
fact that the panel is older is a plus. The simplicity of the older display makes it an
excellent example for learning to use even the most modern graphical LCD displays. The
LM211 operates in the same way as current laptop monitors work. Another good feature
of the LM211 is that although it does not come with hardware to decipher codes like a
text display, the hardware needed to drive the device is minimal. This is because the
LM211 has a simple design. Understanding how the LM211 works is not difficult. It
actually is quite logical and methodical.
3.2 Construction of the LM211 Graphical LCD Display
The LM211 has a very simple design. This design along with all hardware components is
listed below. It would be helpful to obtain a LM211 panel to use while reading this
section.
pin connections
pin connections
240 pixels
64 pixels
240 pixels
Display Area
Figure 3.1: Front View of the LM211 Graphical LCD Panel
A6
A4
A2
A12
A10
A8
A6
A3
A1
A11
A9
A7
B1
B2
B: MSM5239 Shift Register A: MSM5238 Shift Register
Figure 3.2: Rear View of the LM211 Graphical LCD Panel
Figure 3.3 Side View of the LM211 Graphical LCD Display
MSM5238 32 Dot Common Driver: The devices labeled B1 and B2 above belong to this
family of shift registers. The MSM5238 is a 32 bit shift register. Two of the devices are
put in series to represent the 64 rows of the panel.
MSM5839 40-Dot Segment Driver: The devices in Diagram 2 labeled A1-A12 belong to
this family of shift registers. These 12 registers control the horizontal movement of data.
This spans 480 pixels.
3.3 Voltage Source Requirements for the LM211 Panel
The LM211 has 4 voltage inputs. They are listed with their function in the table below.
Pin
7
8
9
10
Voltage Level
4.75-5 V
0V
-8.5—9 V
Symbol
Vdd
Vss
Vee
Vo
Function
Power Supply
Ground
Power Supply for LC driving
Operating Voltage for LC Driving
Table 3.1 Voltage Supplies for the LM211
Vdd is the voltage source that powers all the circuitry on the back of the panel. This
includes the shift registers and capacitors.
Vss is the ground for the board.
Vee is the voltage used to power the LC driving circuitry. This circuitry is separate from
the shift registers on the back of the panel.
Vo is the voltage that causes the liquid crystal to change from dark to light. This is the
Liquid Crystal driving voltage.
All of the above voltages are required for proper operation of the LCD panel.
3.4 Input Signals for the LM211 Panel
There are 4 input signals for the LM211. They are listed below with a description of their
function.
Pin
1
2
Name
D1
FLM
3
4
5
6
M
CL1
CL2
D2
Function
Data line for left half of the screen
Indicates the beginning of a new Display
Cycle
Control Signal for AC Driving
Latches serial data into the shift Registers
Clock signal for shifting the serial data
Data input for right half of the screen
Table 3.2: Input Signals for the LM211
D1 and D2 are the input lines for data. Bits are taken serially, so to fill an entire half of
the screen, the panel needs to be given 15360 different bit values.
CL2 is the master clock for the entire circuit. Each clock of CL2 represents a bit being
shifted from D1 and D2 into the horizontal shift registers. Since there are 240 pixels on
each half of the screen, this clock iterates 240 times filling all the pins of the shift
registers.
CL1 latches the data into place. Once the user has specified the 240 bits, they are shifted
into an active mode where they are displayed on the screen.
FLM determines which vertical line on the screen is active. FLM is high one time every
64 CL1 pulses. This high value is then passed down through the shift register. In this
way, every line will be high one time through the entire screen refresh.
M is a signal used to keep the liquid crystal from breaking down. If direct current is
constantly applied to the panel, the crystal will be damaged and will no longer be able to
change from dark to light. By alternating the direction the current flows through the
panel, the panel is protected from thermal breakdown.
3.5 The LM211DVR Xilinx Module
The LM211 is nothing more than a display panel. It does not have an on panel controller
chip. Thus, the signals specified above must be implemented externally and applied to
the panel. This is achieved in one form in the LM211DVR circuit. This circuit created
Cl1,Cl2,M,and FLM. In addition to these signals, the module allows for a 1 byte input
that specifies data to be displayed on the screen. This data is manipulated by functions
within the module to produce different patterns on the screen. The module has an
onboard ram. The user can write to this ram and store information in the controller chip.
All these details will be explained in detail below.
The first important step to understanding the LM211DVR is to master the protocol. The
onboard memory in the LM211DVR circuit provides the user with 64 bit memory, 8 bits
square. This is known as a glyph. Only 1 glyph can be displayed at a time. The glyph
originally appears at the 0 location on the screen. The LM211 is capable of writing a bit
in the glyph, shifting the glyph, zooming or shrinking the glyph, inverting all bits on the
screen, and of tiling the screen.
The above diagram is of the LM211DVR module. There are 9 input signals and 6 output
signals. When the user wants to write to the panel, a byte of data corresponding to the
desired function is chosen from the protocol and placed on lines in0-in7. Note that in0 is
the least significant bit. Once the data is correctly placed on the input lines, the
handshake signal is pulsed. This lets the data enter the LM211DVR circuit. This
information is stored in flip flops and the specified operation is carried out. The 5
outputs are the control signals specified earlier, CL2, CL1, FLM, M and the data lines D1
and D2. The control signals continually output to the screen causing the screen to be
updated according to what is stored in the internal ram. The data lines output this
information and put it on the screen according to what functions the user has chosen.
3.6 Sub-Modules of the LM211DVR Circuit:
There are 9 Sub-Modules on the LM211DVR circuit. They are listed in the table below
with their function.
CONTROLREG
ZOOMREG
SHIFTREG
VSHFTR
SHIFTER
ZOOM
TILE
GRAPDISP
SIGNALS
Holds the data related to the on/off, tile, and invert bits.
Holds the amount of zoom desired.
Holds the amount of shift required.
Shifts the vertical bits.
Shifts the horizontal bits.
Zooms the glyph according to how much zoom is requested in
ZOOMREG
Repeats the glyph every 8 pixels.
Contains the SIGNALS module and the power supplies for that
module
Creates the signals CL1, CL2, FLM, M and DI, D2
Table 3.3: Modules in LM211DVR
As can be seen in Diagram 6, the LM211 module is broken into sub-modules. Each
module has a specific task. This section describes the modules in the order they are
encountered by actual data.
CONTROLREG is the first module to study. The protocol used to activate this register is
as follows. 00001OTIX. The first 5 bits are a pattern that activate the control register.
The O determines whether the screen is on or off ( 1 for on 0 for off), the T determines if
the screen is tiled or not (1 for not tiled and 0 for tiled) and the I determines whether the
screen is inverted or not ( 0 for not inverted and 1 for inverted). For instance, a 00001110
would tell the circuit to turn onn, invert the bits and tile the screen. Since the first 5 bit
pattern is unique to this module, the zoom, shift and write capabilities will not be
affected.
ZOOMREG is the next module to study. The protocol for zoom is 000000DML. The D
stands for which direction the zoom is desired( 0 for vertical and 1 for horizontal). The
M and L refer to the most and least significant bits of the zoom. Four different zoom
settings are possible. These settings are 1x, 2x, 4x and 8x. These zooms go from 1x at
ML = 00 to 8x at ML = 11. Note that this module does not actually do the logic to
implement the zoom, it only stores the user request for zoom. A later module, ZOOM
actually calculates the zoom.
ZOOM actually implements the zoom command. It uses a hardware zoom. By shifting
what lines are being input as the least significant bit, the size of the glyph will be
changed.
SHIFTREG is similar to ZOOMREG in that it does not actually zoom, it only holds the
users request for a shift. The modules VSHIFTR and SHIFTER actually do the shifting
logic. SHIFTREG has a protocol that is more complicated than ZOOMREG. Since up to
8 bits can be specified in a shift, we need to use 2 bytes. Because of this, the vertical
shift and horizontal shift are broken into upper and lower halves. The vertical shift
protocol for the upper half is 0101DDDD and the lower is 0011DDDD where D can be
set to 1 or 0. The protocol for a horizontal shift is 0001DDDD and 0100DDDD where D
can be set to 1 or 0. These values are stored in d flip-flops so they will be implemented
when the input changes.
VSHIFTR and SHIFTER are the modules that shift the data on the screen. The amount
of shift is received from the SHIFTREG flip-flops.
TILE is a large and gate that determines whether the user wants the glyph in memory
repeated across the screen. If tiling is wanted, the same glyph will be covering the
screen.
GRAPDISP and SIGNALS can be grouped together. They output the signals that control
data flow to the panel. These signals are namely CL1, CL2, FLM and M. These signals
are generated using ABEL HDL. This is because of the complex relationship between
the signals. Implementing the same signals using only schematics would have been quite
difficult and confusing. By using ABEL, a single counter can be used and different areas
of the counter can be correlated to certain signals.
3.7 Protocol for the LM211DVR Circuit
The following protocol is for the input lines of the LM211DVR circuit.
Data Input
msb
lsb
00001OTI
Operation
0101DDDD
Set Control Register Flip Flops according to O,T and I
O ( 0 screen off, 1 screen on)
T ( 0 tile on, 1 tile off)
I ( 0 invert off, 1 invert on)
Set Vertical Zoom Register Flip Flops according to DD
DD 00 no zoom
01 2x zoom
10 4x zoom
11 8x zoom
Set Horizontal Zoom Register Flip Flops according to DD
DD 00 no zoom
01 2x zoom
10 4x zoom
11 8x zoom
Set pixel at Address AAAAAA
D = 0 pixel off
D = 1 pixel on
Set Vertical High Shift Bits according to DDDD
0011DDDD
Set Vertical Low Shift Bits according to DDDD
0100DDDD
Set Horizontal High Shift Bits according to DDDD
0001DDDD
Set Horizontal Low Shift Bits according to DDDD
000000DD
000001DD
1DAAAAAA
Table 3.4: Protocol for LM211DVR
4. Aggregating Separate Components
The serial buffer and separate LCD controllers are to be integrated into one complete
module capable of receiving serial data and displaying text and graphical information on
the LCD displays. The serial buffer is a global device that can generate data for different
types of controllers. In this project, the serial buffer is able to communicate with both a
graphical and a text LCD controller. Each controller has an eight-bit input and a strobe
signal. The serial buffer places data on the eight data lines and sends a strobe signal
indicating that the data is valid. The controllers then take the data and use it per their
design. The serial buffer does not know what the data being sent is to be used for. It
does not care. Its job is to send the data to the controllers.
Appendix A: Figures for Serial Buffer
Appendix B: Figures for text LCD Display and Controller
Appendix C: Figures for Graphical LCD Display and
Controller
Appendix D: Hitachi LM211 Data Sheet
APPENDIX E: Shift Register Data Sheets