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©2008 The McGraw-Hill Companies, Inc. All rights reserved. Digital Electronics Principles & Applications Seventh Edition Chapter 6 Encoding, Decoding,

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Presentation on theme: "©2008 The McGraw-Hill Companies, Inc. All rights reserved. Digital Electronics Principles & Applications Seventh Edition Chapter 6 Encoding, Decoding,"— Presentation transcript:

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2 ©2008 The McGraw-Hill Companies, Inc. All rights reserved. Digital Electronics Principles & Applications Seventh Edition Chapter 6 Encoding, Decoding, and Seven-Segment Displays Roger L. Tokheim ©2008 The McGraw-Hill Companies, Inc. All rights reserved.

3 INTRODUCTION The BCD Code The Excess-3 Code The Gray Code The ASCII Code Encoders Seven-segment Displays Seven-segment LED Displays Decoders BCD-to-Seven- Segment Decoder/ Driver Liquid Crystal Displays Vacuum Fluorescent Displays

4 ©2008 The McGraw-Hill Companies, Inc. All rights reserved. The 8421 BCD Code BCD stands for Binary-Coded Decimal. A BCD number is a four-bit binary group that represents one of the ten decimal digits 0 through 9. Example: Decimal number BCD coded number

5 ©2008 The McGraw-Hill Companies, Inc. All rights reserved. Convert the BCD coded number into decimal. QUIZ Decimal Number BCD Coded Number

6 ©2008 The McGraw-Hill Companies, Inc. All rights reserved. Convert the decimal number 350 to its BCD equivalent. Decimal Number BCD Coded Number QUIZ

7 ©2008 The McGraw-Hill Companies, Inc. All rights reserved. The Excess-3 Code Add 3 to each digit of decimal and convert to 4-bit binary form A BCD code (not 8421 BCD) Decimal Binary +3 Excess Decimal Sample Problem: Excess

8 ©2008 The McGraw-Hill Companies, Inc. All rights reserved. QUIZ 1. To form an excess-3 coded number, decimal 3 is added to the decimal number and this is converted to its 4-bit binary code. (True or False) True 2. The excess-3 BCD number equals __________ in decimal The decimal number 428 equals what excess-3 number

9 ©2008 The McGraw-Hill Companies, Inc. All rights reserved. The Gray Code The Gray codes most important characteristic is that only one digit changes as you increment or decrement the count. The Gray code is commonly associated with input/output devices such as an optical encoder of a shafts angular position. The Gray code is NOT a BCD code. Decimal Gray code

10 ©2008 The McGraw-Hill Companies, Inc. All rights reserved. QUIZ 1. The Gray code is not a type of BCD code. (True or False) 2. The most important characteristic of the ____________ (BCD, Gray code) is that only one digit changes state as you increment or decrement the count. 3. The Gray code is commonly associated with input/output devices such as an optical encoder of a shafts angular position. (True or False) True Gray code True

11 ©2008 The McGraw-Hill Companies, Inc. All rights reserved. The ASCII Code ASCII is an acronym for American Standard Code for Information Interchange Represents numbers, letters, punctuation marks and control characters Standard ASCII is a 7-bit code (127 characters) Extended ASCII (IBM ASCII), an 8-bit code, is also very popular Extended ASCII adds graphics and math symbols to code (total of 256 symbols)

12 ©2008 The McGraw-Hill Companies, Inc. All rights reserved. QUIZ 1. A common 7-bit code used to represent numbers, letters, punctuation marks, and control characters is known by the acronym __________. 2. The acronym ASCII stands for __________________________. 3. Extended ASCII code is a(n) __________ (8-bit, 10-bit) code which adds graphic and math symbols to ASCII for a total of 256 symbols. ASCII American Standard Code for Information Interchange 8-bit

13 ©2008 The McGraw-Hill Companies, Inc. All rights reserved. Electronic Encoder - Decimal to BCD 0 Decimal to BCD Encoder BCD output Decimal input Encoders are available in IC form. This encoder translates from decimal input to BCD output.

14 ©2008 The McGraw-Hill Companies, Inc. All rights reserved. Seven Segment Displays LCD (liquid crystal display) Commonly dark characters on a silvery background Very low power consumption Viewing only OK in good light Backlighted displays can be viewed in low light LED (light emitting diode) display High power consumption Viewing best under low light conditions Commonly red but available in other colors VF (vacuum fluorescent) display Commonly blue-green display (without filters) Medium power consumption Viewing good from dark to lighter conditions Based on vacuum tube triode technology

15 ©2008 The McGraw-Hill Companies, Inc. All rights reserved. QUIZ 1. The type of 7-segment display based on vacuum tube technology which usually has blue-green characters and can be viewed in dark to lighter conditions is the vacuum fluorescent display (VF). (True or False) 2. The type of 7-segment display that shows dark characters on a silvery background, uses very little power, and is good for viewing in bright light is called the liquid crystal display (LCD). (True or False) 3. The seven-segment LED display is best viewed in very bright sunlight. (True or False) True False

16 ©2008 The McGraw-Hill Companies, Inc. All rights reserved. 7-Segment LED Display Operation Limiting resistors 7-segment LED display (common anode) H L b L c H +5Vag Inputs 7-segment code Common anode Cathode terminals (a thru g) b & c inputs active therefore segments b & c light on display Note that inputs are active-LOW 7-segment display reads decimal 1 (segments b & c are lit)

17 ©2008 The McGraw-Hill Companies, Inc. All rights reserved. L a L b L c H +5V a g Inputs 7-segment code Q #1- What will be the decimal output on the 7-segment LED display? Q #2- What is the decimal output on the display for the new set of inputs? L a H L c L d H L f L g L a L b L c L d L e L f L g Q #3- What is the decimal output on the display for the new set of inputs?Q #4- What is the decimal output on the display for the new set of inputs? H L b L c H L f L g QUIZ

18 ©2008 The McGraw-Hill Companies, Inc. All rights reserved. BCD-to- 7-Segment Decoder/ Driver Decoders: BCD to 7-Segment Decoder/Driver BCD input 0 0 Decimal output LED Electronic decoders are available in IC form. This decoder translates from BCD to decimal. Decimals are shown on an 7-segment LED display. This IC also drives the 7-segment LED display.

19 ©2008 The McGraw-Hill Companies, Inc. All rights reserved. BCD-to- 7-Segment Decoder/ Driver BCD input Decimal output ? Q #1- What is the decimal output from the decoder that appears on the 7-segment display? Answer: 3 Q #2- What is the decimal output from the decoder that appears on the 7-segment display? 0 0 Answer: 0 Q #3- What is the decimal output from the decoder that appears on the 7-segment display? Answer: 9 Q #4- What is the decimal output from the decoder that appears on the 7-segment display? Answer: Q #5- What is the decimal output from the decoder that appears on the 7-segment display? Answer: QUIZ

20 ©2008 The McGraw-Hill Companies, Inc. All rights reserved. Liquid C rystal Displays LCDs control available light (do not generate light) Nematic fluid (also called liquid crystal fluid) is sandwiched between two glass plates Monochrome twisted-nematic field-effect LCDs display dark figures on a silvery background. LCDs are commonly used on watches, calculators, and laptops. LCD monitors and TVs are becoming common. Color LCDs use either passive-matrix or active-matrix technology. Active-matrix color LCD screens are more expensive. Active-matrix color LCD screens use thin-film transistors (TFT) and red, green, blue, and white filters. Most laptop screens are backlighted for brightness.

21 ©2008 The McGraw-Hill Companies, Inc. All rights reserved. 100 Hz out-of-phase signal activates segment Metalized segmentsLiquid crystalMetalized layer Glass backplane Polarizer Contacts Liquid Crystal Display PolarizerConductive pattern on glass

22 ©2008 The McGraw-Hill Companies, Inc. All rights reserved. QUIZ 1. While VF and LED displays emit light, LCDs __________ (control available, sublimate red) light. 2. The nematic fluid sandwiched between the glass plates of a LCD is also called _______ _______ (green phosphor, liquid crystal). 3. Monochrome twisted-nematic field-effect LCDs display __________ (dark, white) figures on a silvery background. 4. Liquid crystal displays are difficult to read under low light conditions however most laptop computer flat screens are backlighted to add brightness. (True or False) control available liquid crystal dark True

23 ©2008 The McGraw-Hill Companies, Inc. All rights reserved. a b c d e f g CommonPhase 100 Hz Clock LCD driver The LCD segments with out-of-phase signals are active (a, b, & c are active) Driving an LCD Display BCD Input

24 ©2008 The McGraw-Hill Companies, Inc. All rights reserved. QUIZ Q#1: What is the output on the LCD display? 100 Hz Clock ? BCD Input ABCDEFGABCDEFG LCD Driver LCD Common ANS: 2 Q#2: What is the output on the LCD display? ANS: 0 Q#3: What is the output on the LCD display? ANS: 5

25 ©2008 The McGraw-Hill Companies, Inc. All rights reserved. Vacuum Fluorescent Displays VF displays are commonly used in automobiles because they operate at the proper voltages, have a pleasing blue-green color, are easy to see even when viewed under lower light conditions, and will operate at wide extremes of temperature. VF displays are based on an older triode vacuum tube technology. VF displays are also commonly used in point-of- sale terminals and some desktop calculators.

26 ©2008 The McGraw-Hill Companies, Inc. All rights reserved. QUIZ 1. A vacuum fluorescent display is based on an older vacuum tube technology and is commonly referred to as a _____ _________ (TFT display, VF display). 2. One of the most common applications of VF displays is in _________________ (flat-screen laptop computer screens, automobiles). 3. The VF display has the advantage of being easily readable in either light or dark conditions. (True or False) VF display automobiles True

27 ©2008 The McGraw-Hill Companies, Inc. All rights reserved. Vacuum Fluorescent Display K G f a e g d c b K Cathodes (heaters) Grid Glass back Plates

28 ©2008 The McGraw-Hill Companies, Inc. All rights reserved. QUIZ B C Q#1- The thin wires at A are called heaters or ___. A ANS: Cathodes Q#2- The segments at B are called ___. ANS: Plates Q#3- The screen like section at C is called the ___. ANS: Grid

29 ©2008 The McGraw-Hill Companies, Inc. All rights reserved. PaPa PbPb PcPc PdPd PePe PfPf PgPg +12 V 0 V To light a segment: 1. Heaters must be hot 2. Grid must be at +12V 3. Plate must be at +12V Operating a VF 7-Segment Display Plates Cathodes (heaters) Cathodes (heaters) Cathodes (heaters) Cathodes (heaters) Grid

30 ©2008 The McGraw-Hill Companies, Inc. All rights reserved. QUIZ A B C Q#1- Part A is the ___. Schematic diagram of VF display with heaters connected to battery. ANS: grid Q#2- Part B points at the heaters or ___. ANS: cathodes Q#3- Parts C are the ___. ANS: plates Q#4- The grid is normally at +12V. (T or F) ANS: True Q#5- To light a plate it must be grounded. (T or F) ANS: False Q#6- To light a plate it must be at +12V. (T or F) ANS: True

31 ©2008 The McGraw-Hill Companies, Inc. All rights reserved. REVIEW The BCD Code The Excess-3 Code The Gray Code The ASCII Code Encoders Seven-segment Displays Seven-segment LED Displays Decoders BCD-to-Seven- Segment Decoder/ Driver Liquid Crystal Displays Vacuum Fluorescent Displays


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