Файл: Embedded system development and labs for ARM (R. Muresan, 2005).pdf

Embedded Systems Development and Labs; The English Edition

NOTE: dp – decimal point

4) Display Method

The 8-SEG LED has two ways of displaying and these are static and dynamic.

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Embedded Systems Development and Labs; The English Edition

Static Display: When the 8 SEG LED displays a character, the control signals remain the same.

Dynamic Display: When the 8 SEG LED displays a character, the control signals are alternately changing. The control signal is valid in a period of time (1 ms). Because of the human’s eyes vision, the display of LEDs appears stable.

2. Principles of Circuits

In the circuit of S3CEV40, common anode type of 8-SEG is used. The control signals for each segment are controlled by lower 8 bits of S3C44B0 data bus through 74LS573 flip-latch. The resisters R1-R8 can modify the brightness of the LED. The chip selection for the 74LS573 flip-latch is shown in Figure 4-15.

The flip-latch chip select signal CS6 is generated by S3C44B0 nGCS1 and A18, A19, A20. Shown in Figure 4-16. When nGCS1, A18, A20 are high, and A19 is low, the CS6 is valid. At this time the contents in the lower 8 bits of data bus will be displayed at the 8-SEG LED.

Figure 4-15 S3CEV40 Chip Select Signal Decode Circuit

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Embedded Systems Development and Labs; The English Edition

The start address and end address of the S3C44B0 storage area 1 is fixed. The address range of storage area 1 is 0x02000000-0x2FFFFFF. When the microprocessor accesses this area, the nGCS1 is valid. Compound with A18, A19, A20, CS6 will be valid when the microprocessor accesses the address 0x02140000-0x0217FFFF. In the program, the 8SEG LED is displayed by sending data to the address 0x02140000.

4.6.5 Operation Steps

(1) Prepare the Lab environment. Connect the Embest Emulator to the target board. Connect the target board UART0 to PC serial port using the serial cable that comes with the Embest development system.

2) Run the PC Hyper Terminal (set to 115200 bits per second, 8 data bits, none parity, 1 stop bits, none flow control).

3) Connect the Embest Emulator to the target board. Open the RTC_test.ews project file located in …\EmbestIDE\Examples\Samsung\S3CEV40\8LED_test directory. After compiling and linking, connect to the target board and download the program.

(4) The hyper terminal should output the following messages: Embest 44B0X Evaluation Board (S3CEV40)

8-segment Digit LED Test Example (Please look at LED)

(5)The lab system 8-SEG LED will display 0-F alternately.

(6)After understanding and learning the contents of the lab perform the Lab exercises.

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Embedded Systems Development and Labs; The English Edition

*********************************************************************/

void Digit_Led_Test(void)

{

int i;

/* display all digit from 0 to F */ for( i=0; i<16; i++ )

{

Digit_Led_Symbol(i); Delay(4000);

}

}

4.6.7 Exercises

Write a program that displays each segment of the 8-SEG LED alternatively.

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Embedded Systems Development and Labs; The English Edition

Chapter 5 Human Interface Labs

5.1 LCD Display Lab

5.1.1 Purpose

●Learn to use the LCD panel and understand its circuit functionality.

●Learn to program the S3C44B0X LCD controller.

●Through the Lab, learn to displaying text and graphic on the LCD.

5.1.2 Lab Equipment

● Hardware: Embest S3CEV40 hardware platform, Embest Standard/Power Emulator, PC. ● Software: Embest IDE 2003, Windows 98/2000/NT/XP operation system.

5.1.3 Content of the Lab

Learn to use the S3CEV40 16 Gray Scale LCD panel (320 x 240 pixels) controller. Understand the human interface programming methods based on the LCD display.

●Draw multiple rectangles.

●Display ASCII characters.

●Display a mouse bitmap.

5.1.4 Principles of the Lab 1. LCD Panel

LCD (Liquid Crystal Display) is mainly used in displaying text and graphic information. The LCD device is highly popular for human interface development due the fact that the device is thin, small size, low power, no radiation, etc.

1) Main types of LCD and Parameters

(1) STN LCD Panel

The STN (Super Twisted Nematic) LCD panel displays in light green or orange color. STN LCD panel is a type of liquid crystal whereas the alignment surface and therefore the LC molecules are oriented 90° from each surface of glass. This device produces images in two modes: Positive and Negative. Positive Mode provides white background with black segments. Negative Mode provides black background and white segments. When two polarizing filters are arranged along perpendicular axes, as in the first illustration, light passes through the lead filter and follows the helix arrangement of the liquid crystal molecules. The light is twisted 90 degrees, thus allowing it to pass through the lower filter. When voltage is applied, however, the liquid crystal molecules straighten out of their helix pattern. Light is blocked by lower filter and the screen appears black because of there being no twisting effect.

(2) TFT Color LCD Panel

TFT (Thin Film Transistor) color LCD panels are widely used in computers like notebook computers and monitors.

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