Codes in Digital Systems. This information sheet purposes to explain details on codes involved in digital systems. The explanations related on the types of codes obviously been used, function of Binary Coded Decimal (BCD) and emphasis the arithmetic operations in Binary Coded Decimal other than steps to convert the number from decimal.

1. INSTITUT KEMAHIRAN MARA BESUT
JALAN BATU TUMBUH, ALOR LINTANG,
22000 BESUT,
TERENGGANU DARUL IMAN.
INFORMATION SHEET
( KERTAS PENERANGAN )
PROGRAM’S CODE &
NAME/ KOD DAN NAMA
PROGRAM
EE-021-2:2012 INDUSTRIAL ELECTRONICS
LEVEL/ TAHAP L2
COMPETENCY UNIT NO.
AND TITLE/ NO. DAN
TAJUK UNIT
KOMPETENSI
C02 INSTRUMENT AND TEST EQUIPMENT SETUP &
HANDLING
WORK ACTIVITIES NO.
AND STATEMENT/ NO.
DAN PENYATAAN
AKTIVITI KERJA
1. IDENTIFY INSTRUMENT AND TEST EQUIPMENT
SET UP & HANDLING
2. PREPARE FOR INSTRUMENT AND TEST
EQUIPMENT SET UP & HANDLING
3. SET UP INSTRUMENT AND TEST EQUIPMENT
4. PERFORM RECORDING AND TAGGING OF
INSTRUMENT & TEST EQUIPMENT
5. REPORT INSTRUMENT AND TEST EQUIPMENT SET
UP & HANDLING
CODE NO. / NO. KOD EE-021-2:2012-C02/P(3/15)
Page/ Muka Surat: 1
Of / Drpd : 10
TITLE/ TAJUK:
CODES IN DIGITAL SYSTEMS
PURPOSE/ TUJUAN:
This information sheet purposes to explain details on codes involved in digital systems.
The explanations related on the types of codes obviously been used, function of Binary
Coded Decimal (BCD) and emphasis the arithmetic operations in Binary Coded Decimal
other than steps to convert the number from decimal.

2. INFORMATION/ PENERANGAN:
BINARY CODED DECIMAL (BCD)
Binary coded decimal (BCD) is a way to express each of the decimal digits with a
binary code. There are only ten cod groups in the BCD system, so it is very easy to
convert between decimal and BCD. Because we like to read and write in decimal,
the BCD code provides an excellent interface to binary system. Examples of such
interfaces are keypad inputs and digital readouts.
Binary coded decimal means that each decimal digit 0 through 9 is represented by a
binary code of four bits. All you have remember are the ten binary combinations that
represent the decimal ten digits as shown in Table 1.
The six code combinations that are not used or invalid code are 1010, 1011, 1100,
1101, 1110 and 1111. To express any decimal number in BCD, simply replace each
decimal digit with the appropriate 4-bit code.
DECIMAL DIGIT BCD
0 0000
1 0001
2 0010
3 0011
4 0100
5 0101
6 0110
7 0111
8 1000
9 1001
Table 1: Decimal to BCD Conversions
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3. Example: Convert each of the following decimal numbers to BCD.
a. 35 b. 98 c. 170 d. 2469
Solutions:
a. 3 5 b. 9 8
0011 0101 1001 1000
c. 1 7 0 d. 2 4 6 9
0001 0111 0000 0010 0100 0110 1001
Example 2: Convert each of the following BCD codes to decimal.
a. 1000 0110 b. 0011 0101 0001
8 6 3 5 1
c. 1001 0100 0111 0000
9 4 7 0
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4. BCD is a numerical code and can be used in arithmetic operation. Addition is the most
important operation because the other three operations (subtraction, multiplication and
division) can be accomplished by the use of addition.
Step procedures to add BCD number.
Step 1: Add the two BCD number using rules for binary addition.
Step 2: If a 4-bit sum is equal or less than 9, it is a valid BCD number.
Step 3: If a 4-bit sum is greater than 9, or if a carry out of the 4-bit group is
generated, it is an invalid result. Add 6 (0110) to the 4-bit sum in order to
skip the six invalid states and return the code to BCD. If a carry result
when 6 is added, simply add the carry to the next 4-bit group.
Example: Add the following BCD numbers.
a. 0011 + 0100 b. 0010 0011 + 0001 0101
0011 0010 0011
+ 0100 + 0001 0101
0111 0011 1000
c. 1000 0110 + 0001 0011
1000 0110
+ 0001 0011
1001 1001
d. 0100 01010000 + 0100 0001 0111
0100 0101 0000
+ 0100 0001 0111
1000 0110 0111
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5. Example: Add the following BCD numbers.
a. 1001 + 0100
1001
+ 0100
1101 Invalid BCD number (>9)
+ 0100 Add 6
0001 0011 Valid BCD number
1 3
b. 1001 + 1001
1001
+ 1001
1 0010 Invalid because of carry
+ 0110 Add 6
0001 1000
1 8
c. 0001 0110 + 0001 0101
0001 0110
+ 0001 0101
0010 1011 Right group is invalid (>9), left group is valid
+ 0110 Add 6 to invalid code. Add carry to next
0011 0001 group.
3 1
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6. d. 0110 0111 + 0101 0011
0110 0111
+ 0101 0011
1011 1010 Both groups are invalid (>9)
+ 0110 0110 Add 6 to both groups
0001 0010 0000 Valid BCD number
1 2 0
AMERICAN STANDARD CODE FOR INFORMATION INTERCHANGE (ASCII)
ASCII is the abbreviation for American Standard Code for Information Interchange.
Pronounce “askee”. ASCII is a universally accepted alphanumeric code used in most
computers and other electronic equipment. Most computer keyboards are standardized
with the ASCII. When we enter a letter, a number or control command, the
corresponding ASCII code goes into the computer.
ASCII has 128 characters and symbols represented by a 7-bit binary code. Actually
ASCII can be considered an 8-bit code with the MSB always 0. This 8-bit code is 00
through 7F in hexadecimal.
The first thirty-two ASCII characters are non-graphic commands that are never printed
or displayed and are used only for control purposes. Examples of the control characters
are “null”, “line feed”, “start of text” and “escape”. The other characters are graphic
symbols that can be printed or displayed and include the letters of the alphabet
(lowercase and uppercase), the ten decimal digits, punctuation signs and other
commonly used symbols.
Table 2 is a listing of the ASCII code showing the decimal, hexadecimal and binary
representations for each character and symbol. The left section of the table lists the
names of the 32-control character (00 through 1F hexadecimal).
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7. Table 2: ASCII Representations.
The first thirty-two codes in the ASCII table represent the control characters. These are
used to allow devices such as a computer and printer to communicate with each other
when passing information and data. The extended ASCII contains characters in the
following general categories:
• Foreign (non-English) alphabetic characters
• Foreign currency symbols
• Greek Letter
• Mathematical symbols
• Drawing characters
• Bar graphing characters
• Shading character
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8. QUESTION/ SOALAN:
Answer all the questions.
1. Convert the following decimal to BCD.
i. 34 = ________________________________________
ii. 11 = ________________________________________
iii. 29 = ________________________________________
iv. 151 = ________________________________________
v. 253 = ________________________________________
vi. 540 = ________________________________________
vii. 762 = ________________________________________
viii. 385 = ________________________________________
ix. 930 = ________________________________________
x. 496 = ________________________________________
2. Compute the following BCD operations.
i. 0010 + 1101.
ii. 1001 + 0001.
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9. iii. 0101 + 1000.
iv. 0010 0110 + 0000 1000.
v. 0010 0011 + 0001 0111.
vi. 1001 0000 + 1001 0001.
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10. REFERENCE/RUJUKAN:
1. Ronald J. Tocci (Fifth Edition, 2008). Prentice Hall International., Digital System
– Principle and Application. Pages : 132 till 150.
2. Tocci., Widmer., Moss (Tenth Edition, 2013). Pearson International Edition.,
Digital System – Principle and Application. Pages : 115 till 135.
3. Floyd (Ninth Edition, 2010). Pearson Prentice Hall., Digital Fundamental. Pages :
145 till 163.
4. Nigel P. Cook (2010). Prentice Hall., Introductory Digital Electronic. Pages : 112
till 125.
5. William Kleitz (Fifth Edition, 2011)., Prentice Hall., Digital Electronics – A
practical Approach. Pages : 110 till 132.
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