An Efficient SOC approach to Design CRT controller on

ISSN No: 2348-4845
International Journal & Magazine of Engineering,
Technology, Management and Research
A Monthly Peer Reviewed Open Access International e-Journal
An Efficient SOC approach to Design CRT controller
on CPLD’s
Sudheer Kumar Marsakatla
Prof. Chandrasekhar Narikadamalli Student,
Department of ECE,
ACE Engineering College, Hyderabad.
The design of CRT controller is studied, which is applied
in the Speech Interactive System based on ASIC.CRT
controller based on CPLD is presented. MCU flexible
read and write to RAM with CPLD. Meanwhile, the simulation is also given based on Maxplus. The simulating
results prove that the design can reach the demand of
real time exchanging, and has integrality, reliability and
good applications in the Speech Interactive System.
The main function is to form the address code of character buffer and attribute memory, and generate horizontal scanning, vertical scanning synchronization signal to the video control logic. Due to the complexity
of co-ordination with the microcontroller and memory
RAM, its peripheral circuits is so large and lack of flexibility. On the one hand, the design of CRT controller
based on CPLD, can improve the integration and reliability of the system; on the other hand, it can significantly enhance design flexibility, especially refresh the
entire screen to less than one second in line with SCM
and through control of the memory RAM read and
write, which is the Motorola 6845 cannot be achieved
and is an important innovation of this design.
This is the part of the oscilloscope that displays the input signal as a trace. By this stage, most of the work
has already been done by the vertical and horizontal
circuitry stages. The display circuitry is essentially the
Cathode Ray Tube (CRT) and the graticule, which is the
calibration marking.
M.Tech, Ph.d,FIE,
Department of ECE,
ACE Engineering College, Hyderabad.
The CRT section consists of an electron gun, vertical
and horizontal deflection plates, and the coating that
produce the visual colors. The CRT’s electron gun produces a stream of electrons. These are accelerated to
the front end of the tube and on the way focused into
a narrow electron beam. The vertical and horizontal
plates, mentioned earlier, deflect this narrow beam
of electrons to a particular orientation. This forms the
shape of the input signal. The display end of the tube
has a coating which when struck by this electron beam
emits a particular colour (usually green). This is the
trace, which appears on the display end of the tube.
CRT-based VGA displays use amplitude-modulated moving electron beams (or cathode rays) to display information on a phosphor-coated screen. LCD displays use
an array of switches that can impose a voltage across
a small amount of liquid crystal, thereby changing light
permittivity through the crystal on a pixel-by-pixel basis. Although the following description is limited to CRT
displays, LCD displays have evolved to use the same
signal timings as CRT displays (so the “signals” discussion below pertains to both CRTs and LCDs).
Color CRT displays use three electron beams (one
for red, one for blue, and one for green) to energize
the phosphor that coats the inner side of the display
end of a cathode ray tube (see illustration). Electron
beams emanate from “electron guns” which are finelypointed heated cathodes placed in close proximity to
a positively charged annular plate called a “grid”. The
electrostatic force imposed by the grid pulls rays of energized electrons from the cathodes, and those rays
are fed by the current that flows into the cathodes.
Volume No: 1(2014), Issue No: 12 (December)
December 2014
Page 106
ISSN No: 2348-4845
International Journal & Magazine of Engineering,
Technology, Management and Research
A Peer Reviewed Open Access International Journal
Much of the potential display time is therefore lost in
“blanking” periods when the beam is reset and stabilized to begin a new horizontal or vertical display pass.
The size of the beams, the frequency at which the beam
can be traced across the display, and the frequency at
which the electron beam can be modulated determine
the display resolution.
figure.1: cathode ray tube
Between the grid and the display surface, the beam
passes through the neck of the CRT where two coils
of wire produce orthogonal electromagnetic fields. Because cathode rays are composed of charged particles
(electrons), they can be deflected by these magnetic
fields. Current waveforms are passed through the coils
to produce magnetic fields that interact with the cathode rays and cause them to transverse the display surface in a “raster” pattern, horizontally from left to right
and vertically from top to bottom. As the cathode ray
moves over the surface of the display, the current sent
to the electron guns can be increased or decreased to
change the brightness of the display at the cathode ray
impact point.
Display surface:
Figure 3: resolution of display
Video data typically comes from a video refresh memory; with one or more bytes assigned to each pixel location (the Nexys3 uses three bits per pixel).
The controller must index into video memory as the
beams move across the display, and retrieve and apply
video data to the display at precisely the time the electron beam is moving across a given pixel.
A VGA controller circuit must generate the HS and VS
timings signals and coordinate the delivery of video
data based on the pixel clock. The pixel clock defines
the time available to display one pixel of information.
The VS signal defines the “refresh” frequency of the
display, or the frequency at which all information on
the display is redrawn. The minimum refresh frequency is a function of the display’s phosphor and electron
beam intensity, with practical refresh frequencies falling in the 50Hz to 120Hz range.
The number of lines to be displayed at a given refresh
frequency defines the horizontal “retrace” frequency.
For a 640-pixel by 480-row display using a 25MHz pixel
clock and 60 +/-1Hz refresh, the signal timings shown in
the table at right can be derived.
Figure 2: display surface
Information is only displayed when the beam is moving
in the “forward” direction (left to right and top to bottom), and not during the time the beam is reset back to
the left or top edge of the display.
Timings for sync pulse width and front and back porch
intervals (porch intervals are the pre- and post-sync
pulse times during which information cannot be displayed) are based on observations taken from actual
VGA displays.
Volume No: 1(2014), Issue No: 12 (December)
December 2014
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ISSN No: 2348-4845
International Journal & Magazine of Engineering,
Technology, Management and Research
A Monthly Peer Reviewed Open Access International e-Journal
•The controlling of the ADC;
•Controlling the sampling rate.
•Starting a sampling frame in response to a trigger signal.
Figure 4: VGA controller
The ADC used is the 8bit Flash ADC0820, from National
Semiconductor. The timing diagrams of the ADC. I then
wire up the ADC to see that it functions. First a brief
description of how the ADC works.
Starting from the left we have an adjustable attenuator. This module scales the input signal, down or up,
to the input sensitivity of the ADC. The user selects the
scaling factor. This block should have high impedance
in order to minimize the loading of the circuit from
which the input signal is being measured.
This input impedance should also be compatible with
the electrical characteristics of standard scope probes.
Next we have the ADC. This module is responsible for
the conversion of the analogue input signal to its digital form, for further processing.
•The transformation of input digital data from ADC, to
a form that can be displayed on a VGA monitor;
•The controlling of the VGA monitor.
The configuring processor configures the CPLD at start
up. This could be a configuring ROM, especially made
for this function, or a simple microprocessor. Finally,
the interface electronics simply provides the appropriate signal levels for the VGA monitor control lines. The
Memory module of the CPLD system.
General description of Memory module:
Memory is a passive system, in that it is completely
controlled by processes external to it. It is also a relatively simple module. Figure 8.1 shows a complete
breakdown of Memory.
The conversion rate should be as fast as possible as it
has a direct bearing on the bandwidth of the scope. A
faster conversion rate implies a faster sampling time,
and thus a higher range of frequencies that can be
The trigger controller is responsible for the selection of
the triggering modes of the oscilloscope. The user sets
the trigger mode and level. This should be designed
with high impedance to minimize loading.
The CPLD controller is the brain of the whole system.
Essentially it implements the 2-process architecture
mentioned earlier. The software that describes this
controller will be described in detail in the later chapters. For now it is enough to know that this module is
responsible for:
Figure 5: design of memory module.
The Displayer module of the CPLD system:
This module describes the functionality of the Displayer module. This module takes care of the visuals of the
Description of VGA monitor:
The VGA monitor was explained earlier in more detailed. It is now enough to say that it consists of a 480
x 640 matrix of pixels; RGB data
Volume No: 1(2014), Issue No: 12 (December)
December 2014
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ISSN No: 2348-4845
International Journal & Magazine of Engineering,
Technology, Management and Research
A Peer Reviewed Open Access International Journal
is sent serially to the monitor; and that control is accomplished by setting the VSYNC and HSYNC signals at
the appropriate times.
General description of Displayer module:
Displayer is responsible for conditioning the value of
the data sample stored in memory, in order for it to be
displayed on a VGA monitor. It then goes on to display
the trace stored in memory. Displayer runs continuously. Figure summarizes the Displayer module.
The Working Principle and design parameters of
a CRT Display:
System Structure:
Microcontroller indexes the character dot matrix of
the text information (character code) which will be displayed in the Chinese character dot matrix library ROM
(29C040), when then horizontal and vertical signals retrace period, and extracts 32 bytes of Chinese character
dot matrix data, then deposit them in the 32K display
buffer RAM (62256). 2. The CPLD produces the line synchronization, frame synchronization signal at speed of
72Hz field frequency and 31KHz line frequency, at the
same time generates the address code and read the
dot matrix bytes in the display buffer RAM, then sends
into the shift register and shifts out to the video control logic to form the output signal of the display.
CRT display use lum signal to control the electron gun
eradiating electrons, use two scan signals to control
the electrons shooting the given dot of the screen, so
that a picture forms. The CRT monitor is composed of
five parts, which are electron gun, defection coil, shadow mask, the phosphor layer and scanning circuit.
Raster scan can be used by the electron beam, which
scans point from the top left of the screen, point by
point to the right, then form a horizontal line; to reach
the far right, back to the next horizontal line of the left,
repeat the above procedure. When the electron beam
scans the lower right corner point of scanning, the
frame is formed. Since then, the electron beam back to
the top left of the starting point begin the next frame
scan. In this way the images and texts are displayed on
the monitor.
Figure 6: Horizontal and vertical scan timing
Figure 7: the structure of CRT controller based on
In the video viewing area, the CPLD reads RAM memory
for dot matrix display, while generating inverting field
signal hv_syn is high, so that the microcontroller stops
write character dot-matrix information to the memory.
When the hv_syn signal is low at the inverting blanking
field, the CPLD will output the address switch to the address bus of the microcontroller. The microcontroller
opens the tri-state data bus 245 by movx instruction
and the A15=0, to write dot matrix Chinese character
to the memory RAM, in order to avoid the conflict of
memory read and write data.
Memory ROM, according to Chinese character code
from small to large in turn stores the primary and secondary Chinese character dot matrix. Because the character dot matrix is16×16, so each character takes up 32
bytes. For each Chinese character, to retrieve the corresponding 32 bytes dot-matrix information and then
write to the display buffer RAM.
Volume No: 1(2014), Issue No: 12 (December)
December 2014
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ISSN No: 2348-4845
International Journal & Magazine of Engineering,
Technology, Management and Research
A Monthly Peer Reviewed Open Access International e-Journal
The way of character dot-matrix datum stored in RAM,
is called “screen memory-mapped”, which is each pixel
on the screen corresponds to a RAM storage unit. Because CRT controller display line by line on the screen,
so 32 bytes written to memory is to increase every two
byte address 50H, then the pointer to the next line at
the same colum.
Simulation result of cathode ray tube:
Figure 11: device utilization report of cathode ray tube
Figure 8: simulation result of cathode ray tube
Figure 9: timing report of cathode ray tube
According to the working principle and technical indicators of the display, combined with design requirements, the paper puts forward system parameters
about text display to achieve a CRT controller based
on CPLD, which is achieved by simulating and testing.
The design of CRT controller based on EDA, which is
applied to the digital speech terminals, not only reduces the complexity of the digital electronic system,
but also significantly enhances the flexibility of design,
system integration and reliability. Which is also once
again confirmed Electronic Design Automation (EDA)
technology has infiltrated into the electronic system
and ASIC design chain, the software has been applied
to a variety of electronic design and simulation, the circuit design, adjustment and improvement are more efficient and convenient.
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ISSN No: 2348-4845
International Journal & Magazine of Engineering,
Technology, Management and Research
A Peer Reviewed Open Access International Journal
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