1. Computer Data Formats Microprocessor Course Electrical Engineering Department University of Indonesia

2. ASCII Data

American Standard Code for Information Interchange (ASCII)data represent alphanumeric characters in the memory of a computer system ( Table 1.7 )

The standard ASCII code is a 7-bit code with the eighth and MSB used to hold parity in some systems

ASCII are most often stored in memory using a special directive to the assembler program calleddefine byte(s)or DB

3. BCD Data

Binary-Coded Decimal (BCD) information is stored in either packed or unpacked forms

Packed BCDdata are stored as two digits per byte

Unpacked BCDdata are strored as one digit per byte

The range of a BCD digit extends from 0000 2to 1001 2or 0-9 decimal

Table 1.9shows some decimal numbers converted to bothpacked ad unpacked BCD

4. Byte-Sized Data

Byte-size data are stored asunsignedandsigned integers

Negative signed numbers are stored in the 2s complement form

• Whenever a number is 2s complement, its sign changes from negative to positive or positive to negative

• See example1-22, 1-23

Define bit ( DB )directive is used to store 8-bit data in memory

5. Word-sized Data

A word (16-bits) is formed with two bytes of data

The LSB is always stored in the lowest-numbered memory location, the MSB in the highest (i.e.,little endianformat) -- used with Intel family of microprocessor

An alternate method (i.e.,big endianformat) is used with the motorolla family of micro-processors

6. Word-sized Data

Fig 1.11(a) & (b)shows the weight of each bit position in a word of data

Example 1.25shows several signed and unsigned word-sized data stored in memory using the assembler program

Note thatdefine word(s) directiveorDWcauses the assembler to store words in the memory

7. Doubleword-sized Data

Doubleword-sized data requires four bytes of memory (32-bit number)

Doubleword-sized data appear as a product after a multiplication and also as a dividend before a division

Fig. 1-12shows the form used to store doublewords in the memory and the binary weights of each bit position

To define doubleword-sized data, use assembler directivedefine doublewordorDD

8. Real Numbers

A real number (floating-point number) contains two parts: a mantissa, significand, or fraction and an exponent

Fig. 1-13andexample 1-27depicts both the 4-byte ( single precision ) and 8-byte ( double precision ) forms of real numbers

The exponent is stored as a biased exponent

• an exponent of 2 3 is represented as a biased exponent of 127+3 or 130 (82H) in the single- precision form or as 1026 (402H) in the double-precision form

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