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Design of LED Display Control System Based

on AT89C52 Single Chip Microcomputer


Yongxian Song
The Institute of Electronic Engineering Huaihai Institute of Technology Lianyungang , China

[email protected]



Yuan Feng Juanli Ma and Xianjin Zhang
The Institute of Electronic Engineering Huaihai Institute of Technology Lianyungang , China

[email protected]






Abstract—This paper introduces display design process

about hardware and software based on AT89C52 single chip

microcomputer. We use a simple external circuit to control

the display screen, which size is 32 × 192. The display screen

also can display the size of the six 32 × 32 dot matrix

Chinese characters by a dynamic scan mode, and can be

divided into two small display screen, which can display

twenty-four Chinese characters whose size is 16×16. We can

modify the code to change the content of the display,

subtitles can achieve scrolling function and the scroll speed

can be adjusted according to requirements, subtitles can

also achieve pause function. The Chinese character code

stored in external data memory, the capacity of data

memory is expanded according to the requirements of

Chinese characters we want to show. This display screen has

advantages of small volume, few hardware and simple

circuit structure.

Index Terms—LED, Chinese Character Display, AT89C52

I. INTRODUCTION

LED display has become an important symbol of the

city lighting, modernization and information society with

continuous improvement and beautification of people's

living environment [6]. LED lights can be seen in the

large shopping malls, railway station, docks, underground

station, a variety of management window and so on. LED

business has become a fast-growing new industry, a huge

market space and bright prospects [9]. The text, pictures,

animation and video are displayed by LED’s light, and

content can be changed. Some components are the

display devices of the modular structure, and which

usually consists of a display module, control system and

power system. The display module is constituted by the

lattice structure which consists of LED, and is responsible

for light-emitting display; the screen can display text,

pictures, video and so on by control system which can

control light or dark of LED in the corresponding region;

Power system is responsible for transforming input

voltage an d current into voltage and current which the

screen needs. LED dot matrix display extracted display

character font through PC, and sent to the microcontroller,

then displayed in the dot matrix screen, which mainly

used for display of indoor and outdoor characters. LED

dot matrix display can be divided into graphic display,

image display and video display by displayed content.

Compared with the image display, the characteristics of

graphic display is no difference in gray color whether it is

monochrome or color display. Therefore, graphic display

also fails to reflect the richness of color, and video

display can not only show exercise, clear and full-color

images, but also show television and computer signals.

Although there are some differences between the three,

but the most basic principles are similar [6].

SCM has excellent cost performance, small size, high

reliability, strong control, and widely used in smart

instruments, mechanical and electrical integration, real-

time process control, robotics, domestic appliances, fuzzy

control, communications systems and so on.

This article described the design by the LED display

relevant principle, and the design of hardware and

software structure are described in detail, finally, we

simulate for the overall design and analyze the results.

II. System Overall Structure Design

Single Chip Microcomputer (SCM) models were

selected according to the target, function, reliability, cost,

accuracy and speed of the control system. According to

the actual situation of the subject, the choice of SCM

models mainly considered from the following two aspects:

First, SCM has strong anti-interference ability; Second,

SCM has a higher cost-effective. Due to MCS-51 is

widely used in China, has more information and can

compatible with the more peripheral chips too, in

particular, ATMEL Corporation, introduced a new

generation microcontroller in 2003, that is 89S series,

and its typical products with high performance and low

cost microcontroller is AT89C52. AT89C52 is a low

voltage, high-performance CMOS 8-bit microcontroller,

the chip includes 8 KB read-only program memory

(PEROM) which erase can be repeated, 256byte random

access data memory (RAM), devices adopt high-density

nonvolatile memory technology to produce, compatible





Manuscript received January 1, 2010; revised June 10, 2010;
accepted July 14, 2010.

Page 2

with the standard MCS-51 instruction set and the 8052

products, while the chip built-in general-purpose 8-bit

central processing (CPU) , Flash storage unit, can be

applied to the more complex control applications[10].

The system was realized by the circuitry which is

made up of AT89C52 chip, Clock circuit, reset circuit,

column scan driver circuit, line drive circuit and the six

32 × 32 LED dot matrix, the overall structure of LED

characters display is shown in Fig.1. A display unit is

composed of dot matrix and two 74HC154. Line data

signal is divided into two parts, which is given by the two

8255A respectively, but the 8255A data are from the P0

port the master controller AT89C52. The column

scanning signal of each character was given by the two

74HC154, the 74HC154 12 pieces and was divided into

six groups. The input signal of 74HC154 was given by

the P1.0~P1.3 of AT89C52. External data memory 6264

connected with the AT89C52 the P0 port.



Figure 1 The overall structure of LED characters display

III. SYSTEM HARDWARE CIRCUIT DESIGN

A. Circuit Design of MCU Control System

The size of Chinese characters is 32 × 32, but

microcontroller has 32 I/O port, and can’t meet design

requirements, so the I/O port must expand, the data port

expansion was implemented by two 8255A. The data port

expansion is shown in Fig.2, 74HC373 is the address

latch, and latch low eight address, the low eight address

signals of 6264 provided by it, but the high eight address

signals of 6264 provided by P2.0~P2.4, Internal port of

8255A was chosen by A0 and A1. 74HC139 is 2-4

decoder, whose input signals are provided by P2.6 and

P2.7 of SCM, and provided strobe for the external I / O

devices, because the system has more than one external

device, make sure that they can not be gated, so that their

addresses is the only and do not repeat.

The clock circuit of AT89C52 composed of 18, 19

feet from the clock side (XTALI and XTAL2), and

12MHz crystal X, capacitor C1 and C2, and uses on-chip

oscillator mode.

Reset circuit uses a simple power-on reset circuit, and

mainly constitute of resistor R1, capacitor C3, connected

to the AT89C52's reset input pin.





Figure.2. SCM control system circuit

B The Circuit Design of Display Memory Unit

The size of Chinese characters is 32×32 in the

design, each character composed of four parts which are

(a), (b), (c), and (d), and each part composed of four LED

matrix which the size is 8 × 8, circuit decomposition map

of display unit is shown in Fig.3. The line signals of (a) ~

(b) are given by two 8255A, 1PA0 ~1PA7 and 1PB0

~1PB7 are PA and PB port of 8255A-1, 2PA0 ~ 2PA7

and 2PB0 ~ 2PB7 are PA and PB port of 8255A-2, the

right figures represent column scan signals which is given

by 74HC154. 16 column strobes are provided by

74HC154, (a) ~ (d) requires eight signal, respectively, so

(a) and (b) share a 74HC154, (c) and (d) shared a

74HC154. Display a character need two 74HC154 which

provide column scan signals. When the circuit works, the

(a) ~ (d) is gated by scanning signal in proper order, only

one was gated at a time, and other columns are

extinguished, the displayed data is given by two pieces of

8255A simultaneously, the human eye will see a stable

character because of the human eye's persistence of

vision. In addition, because the Chinese character for

each display needs 128 bytes storage space, but AT89C52

microcontroller chip is only 256 bytes data memory, it is

far less than the design requirements, so we the expanded

storage space by 8K × 8 external data memory 6264.



(a) (b)

JOURNAL OF COMPUTERS, VOL. 6, NO. 4, APRIL 2011 719

© 2011 ACADEMY PUBLISHER

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(c) (d)

Figure.3. Circuit decomposition map of display unit

C The Design of Ranks Data Unit Circuit

Inte1 8255A is a universal programmable parallel

input/output interface chip. Its function can be set through

the software program, and has a strong versatility. It can

be directly through the CPU data bus connected to

external devices, easy to use and flexible. Inte18255A

interface chip has three 8-bit parallel input and output

ports, programming methods can be used to set three

ports as input ports or output ports. Chips work have the

basic input and output, strobe input/output and

bidirectional input / output. When the data were

transmitted by data bus of CPU, its can choose to

unconditionally transfer, query transmission or interrupt

transmission. During Inte1 8255A chip three-port, the

port C can be used as not only the data port, but also the

control port. When the port C is taken as a data port, it

can be used as not only 8-bit data port, but also separately

as two 4-bit data port, and each bit of the port C can be

operated, can set a particular bit to input or output, so

provide convenient conditions for bits control.







Figure.4. Line data unit circuit

In design of the display unit circuit, the lines data are

given by two 8255A, as is shown in Figure 4. This design

uses dynamic display means to display Chinese

characters, which can be controlled the by the means of

line or column scanning, The system uses the method of

column scanning to control screen, Specific column

scanning circuit is shown in Figure 5. Column scanning

circuit composed of 12 pieces of 74HC154.Two pieces of

74HC154 provided 32 strobes to display a character. The

input signal of 74HC154 is P1.0 ~ P1.3 which is provided

by AT89C52 to control screen, but 12 pieces of 74HC154

were used in the design, they work according to the order,

the input of another piece of 74HC154 is P1.4 ~ P1.7

which is provided by AT89C52 to control screen.



Figure.5. column scan unit circuit



Figure.6. Serial Communication Interface Circuit

D Serial Communication Interface Circuit

PC and SCM are linked via a serial communication

interface. In order to implement serial communication

function between MCU and PC, and serial interface level

of SCM will be changed into standard RS-232C level

[11]. Where the output voltage of PC’s RS-232C port is

± 12V. MCU and PC, taking into account the short

distance communication, and microcontroller is mainly

720 JOURNAL OF COMPUTERS, VOL. 6, NO. 4, APRIL 2011

© 2011 ACADEMY PUBLISHER

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responsible for receiving commands and data, so the PC

is directly connected with the microcontroller, this is the

simplest connection method. the signals which is from

PC’s TXD-side were changed into a current signal

through the communication circuit, the infrared light-

emitting diodes of optocouper have current when a signal

occurs, the light signals which is emitted by diode

projected onto the phototransistor, and converted to

electric signal, then input to the microcontroller RXD

side, so photoelectric conversion is implemented, and

electrical is completely isolated to avoid the feedback and

interference which is produced by output side. as is

shown in Figure 6

IV. SOFTWARE DESIGN

The entire software design mainly composes of

display program and communication program. The

Chinese characters to be displayed on the screen,

character and other data for transmission control and

display functions were achieved by dynamic scan. Real-

time communication parts which communicate with PC

receive data information by SCM serial disruption, so

real-time data information transmission with PC was

implemented.

The host computer software was implemented by

Visual Basic. In the standard serial communication,

MSCOMM which is the power communication control is

provided by VB, it can set the serial communication of

data sent and received, and the serial communication port

status, message formats and protocols are set, directly

send data by PC’s RS -232/RS-485 serial port. In order to

realized to PC reliable communication with SCM, and

ensure that both sides have the same data format and

baud rate [11], this design uses RS-232 communications,

a 10 bits data format, 9600bit / s baud rate.

A Principles of Chinese characters dot matrix display

and Sub-codes

Chinese Times New Roman font which is UCDOS

was taken as an example, each word composed of 16 ×16

dot matrix. That is, every word of the national standard

Chinese character library expressed by the 256 lattice.

We can understand each point as a pixel, and the shape of

each word understood as an image. In fact, this character

display screen not only can display Chinese characters,

but also can display any graphics within the scope of 256

pixels. Due to the bus of microcontroller is the 8-bit, and

a word need to split into two parts, as is shown figure 7.

Figure.7. Principles of Chinese characters display

In order to understand Chinese characters dot matrix

composition law, at first, the characters code was

obtained by column scanning method. Chinese characters

are divided into upper part and lower part, the upper part

composed of 8 ×16 lattice, the lower part was also

formed by the 8 ×16 lattice. The first column of the upper

left corner which was the upper part was shown by

Column scanning method first, namely, P00~P07 port of

0 column, direction was P00~P07, Chinese character for

"large" was displayed, P05 was on, the other is off. That

is, binary is 00000100, and convert to hexadecimal as 04h.

After the first column of the upper part was over, and

continue to scan the bottom half of the first column, It

can be seen from Figure 7, this column is not on all, that

is, binary was 00000000, hex was 00h. According to this

method, the second column, third column, until the

sixteenth was scanned in turn. Characters "big" scan code

can be drawn.

04H, 00H, 04H, 02H, 04H, 02H, 04H, 04H

04H, 08H, 04H, 30H, 05H, 0C0H, 0FEH, 00H

05H, 80H, 04H, 60H, 04H, 10H, 04H, 08H

04H, 04H, 0CH, 06H, 04H, 04H ,00H, 00H

It can be seen from this principle, no matter what font

or image display, we can use this method to analyze the

scan code and appears on the screen.

Although above methods allow us to figure out the

code for character dot-matrix process, but rely on manual

methods for character code is a very complicated matter.

To this end, Font software is used to find the character

code, the content to display is entered after the software

opens, font and size can be chosen according to

requirements, you can select modulo by row or by

column. Press the modulus button, the hexadecimal data

character code can be automatically generated, we need

to copy the data into the program.

B. Address Assignment the Port and Data Memory

In this design, we used to 8255A, 6264 and other

external devices, and their gating is not the same, so

strobe is controlled, which involves the address allocation

problem. In the system, the address code of 8255A is

3FFCH ~ 3FFFH and 7FFCH ~ 7FFFH, the address code

of 6264 is 0A000H ~ 0BFFFH. In addition, memory 6264

is divided into four zones, each space size is 2K, the

TABLE I.
8255 AND 6264 ADDRESS ALLOCATION TABLE

Peripheral
devices

A15-A0

The number
of chip

locations

Address
coding

8255A-1
0011 1111 1111 11xx


4 3FFCH~3FFFH

8255A-2 0111 1111 1111 11xx 4 7FFCH~7FFFH

6264
1010 0000 0000 0000~
1011 1111 1111 1111

8
0A000H~0BFFF

H



© 2011 ACADEMY PUBLISHER

Page 5

corresponding address code is 0A000H ~ 0A7FFH,

0A800H ~ 0AFFFH, 0B000H ~ 0B7FFH, 0B800H ~

0BFFFH respectively. Table 1 and table 2 show the

address allocation of the 8255A and 6264 respectively.

C. Software process

Software program composed of the beginning,

initialization, display program, front, which the main

program and subroutine flow chart are shown in Figure.8.

and Figure 9. Character code stored in the static memory

6264, and the SCM will wait for signal is given, that is,

the input signal of SCM pin P3.0. When P3.0 is from low

to high, display program begin to be run. First, control

words written to 8255A control port, 8255A work in the

form of mode 0 in the design. After control word was

finished, the data will be displayed which is transferred to

the 8255A from the 6264, the display data is output for

four times because the line width of the characters screen

is 32, a row of data is input and transported from top to

bottom each, signal of the first rows which is controlled

by SCM is gated after data transmission is over, so the

first column data is displayed, then call delay procedures

to display the contents of the stable. the next column of

data is read after delay procedures is over, and the next

row is gated, so that the second column of data is also

displayed, and so on, because the screen size is 32 × 192,

192 rows are shown, and 192 rows constitute an image.

Then, scanning begin from the first column, and the

starting address of display data backward shift on the

basis of the original, which has an address overflow

issues, it will assign start address to the address pointer

when the data address is overflow, the display data

content will be constantly repeated.

Flow chart of communication with PC and SCM is

shown in Figure 10. Real-time communication parts

which communicate with PC receive data information by

SCM serial disruption, so real-time data information

transmission with PC was implemented.



Figure.8 The flow chart of main program



Figure.9 The flow chart of subroutine

TABLE II.
6264 INTERNAL PARTION TABLE

Zoning

categories
A15~A0

Partition

size

Address

coding

First district
1010 0000 0000 0000~

1010 0111 1111 1111
2K

0A000H~
0A7FFH

Second

district

1010 1000 0000 0000~

1010 1111 1111 1111
2K

0A800~

0AFFFH

Third

district

1011 0000 0000 0000~

1011 0111 1111 1111
2K

0B000H~

0B7FFH

Fourth

district

1011 1000 0000 0000~

1011 1111 1111 1111
2K

0B8000~

0BFFFH



722 JOURNAL OF COMPUTERS, VOL. 6, NO. 4, APRIL 2011

© 2011 ACADEMY PUBLISHER

Page 6

Figure.10 Flow chart of communication with PC and SCM

V. SIMULATION RESULTS AND ANALYSIS

After the hardware and software design finished, the

content of the design was simulated by Proteus, and

modify circuit or optimize the program according to the

simulation results. Proteus software which is EDA tool

software is published by the British Labcenter electronics

companies (the software agent in China is the Guangzhou

Electronic Technology Co. Ltd. vane) [7]. It not only has

simulation functions of other EDA tools, but also

simulates microcontrollers and peripheral devices. It is

the best simulation tool for microcontroller and external

device. Although the Proteus just started in the domestic,

lovers of SCM, the teachers of teaching in SCM and

science and technology workers which engaged in SCM

all love this software. Proteus is the world's leading EDA

tools (simulation software), from the schematic layout,

debugging code to the MCU and the external circuit co-

simulation, a key switch to the PCB design, complete

design was realized from concept to product. It Is only

simulation software platform which is composed of

circuit simulation software, PCB design software and the

virtual model, the processor model supports 8051, HC11,

PIC10/12/16/18/24/30/DsPIC33, AVR , ARM, 8086, and

MSP430, etc. Cortex and the DSP family of processors

were increased in 2010, and will increase other series

processor model. In the compilation side, it also supports

IAR, Keil and MATLAB and so on.

A PCB design and component assembly

Taking into account the number of components used

in this design is not too much, we used the single routing

strategy, and use a small amount of jumper wires on the

top floor. The circuit are not stringent requirements for

components parameters, as long as the component

selection is correct, no damage, good circuit board

manufacturing process, all electronic components can be

assembled into the correct welding procedure, and to

download program and debug program. When PCB

board was produced and debugged, IC that is 20 pin

should be installed in the AT89C52 position, in order to

the microcontroller can take down from the circuit board,

and write program.

B Simulation

Scroll of Chinese characters was implemented by

software programming, we take a whole series of images

which was implemented by Column scan signals to a

frame, here is 192 rows. Then the next frame data

backward shift on the basis of the first frame data, and

dynamic display can be generated. The images result of

the simulation is shown in Figure11.







Figure.11 the images result of the simulation

The simulation results shows that simulation is

consistent with theoretical analysis, the data distribution

of the memory is correct, the data correctly stored into the

data memory, the display shows the contents of the

program is the data to be displayed, the display can also

be achieved pause and display speed is adjustable,

indicating that the design of the hardware and software

are possible.

After the compilation and simulation of program was

accomplished, preparing an editor that can write the

AT89C52, and connected with the host computer

hardware, that is, we can write AT89C52 chip and

download, then, the microcontroller AT89C52 which is

written program insert into the IC that has 40 pins. When

power is connected, we can debug and run,

As the system circuit require for parameters of the

components is not very high, as long as the device is

better, the parameters can meet the requirements, and

work immediately after welding assembly.

VI. CONCLUSION

LED display system that was designed adopted the

host computer and slave structure, the host computer is

PC, and communicated with slave computer display

system through the serial communication interface, which

can implement string modification, display mode settings,

time settings and other functions; The slave mainly

implement display of LED dot matrix display screen

which was controlled by SCM. Chinese character display

JOURNAL OF COMPUTERS, VOL. 6, NO. 4, APRIL 2011 723

© 2011 ACADEMY PUBLISHER

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