( 25 )育教日八十月二十年午庚豆
1991 中學會考預習專欄
明德出版社
MILL & DALE PRESS.
Computer (18)
the number of digits is eight. (2) The nineth bit is.ignored. because the length of ward is limited to 8-bit.
:
(3) 00001000 2 81
''' 21-13 = 8
The answer is verified.
*(4) Only negative number.
represented by 2's complement!
(b) 13qg = 000011012
(4) If
報日僑
more bits' are used for the mantissa which will then be more accurate. If:more bits are used for the exponent then the range of number will be larger.
Floating Point Representation
Flood Point Representation
Range
small
000101012 2110 -2110 11101011.
-32768 to 32767
(16-bit word)
Jargo -38
38
(Accuracy Exact
110 - 10
(8-bit exponent)]
The number of
(12's complement)
(except overflow significant lar underflow)
1310-2110
digits depends on the length of mantisse.
Choy
1340
+ (-2110 000011012 +11101011, 11.1110002
00001101 11101011 11111000
in
e.g.
Subtraction of numbers in two complement representation
A-, B.
(-8)
As negative. numbers are represented in 2's complement format. Therefore suttraction of numbers can be done by adding negative numbers in complement form..
Example:
two's
Perform the following subractions. complement 8-bit word
in
representation:
-(a) 21-13
(b) 13 21
Solution:
(*) 21,0 = 000101011⁄2
1340
= 00001
201701
131011110
100112
Remarks:
(1) The "1" in the first bit from the left may indicate that it is a negative number. It is the sign bit.
(2).The decimal equivalent of the
answer
-128+64+32+16+8:
Floating Point Representation inside. computer:
(1) Numbers
form.
eg.
are
changed to normalized.
1000:1-0-1000110101 (6inary)
0.100001
101
exponent:
Mantissa
(2). Suppose the word
computer word to point humbers are 12 bits. The format to store the above now may be
Tength of the store floating
(5) Truncation and rounding off
floating point numbers
3.141592654...
If 4 decimal places are required for the number, then
1.= 3.1415 (under truncatlon} ii. w=.3.14.16. (after rounding). (a) Both numbers . contain cut off- .errors. But it is worthwhile
in
to notice. the fact that Error in rounding off & Error truncation (b) Overflow error:
e.g. Use 8-bit word tocompute
20810
+ 103 10
11010000
01100111. 100110111*
Carry. bit ignored.
55:0
=
001101112130
The answer is obviously wrong. Similiarly, underflow may also
cause error.
2110
(-1310)
00010101 +11110011.
000101012 + 1111001100001000 000010002
ignored
Remarks:
(1) Preceding zeros are added until
CHOIRE S
I(a) The
̇六期蠱:日二月二 ( 一九九一年十八國民中
excess-16 is used for the exponent. to represent negative exponents.
(b) The actual value of the exponent.
should be compute. by less 16.
e.g. The zerd exponent: P100002
the actual exponent = 15 - 16
e.g. The exponent 10011
the actual exponent = 000112
| (c) If 6 bits are -used for the representation, then excess-32 are
used.
Representation information
Character
ASCII
.48 49
67
Alphanumeric
store, and process both numbers and characters.
Alphanumeric character set (a):10. decimal digits. (b) 26 upper-case.
alphabets.
(c) 26 Tower-case
alphabets..
(d) special characters.
($, +, -, *, ?}
Jetters
letters
- distinctive pattern of bits
(a) EBCDIC (Extended Binary coded.
'B'bits
Decimal Interchange code) BM
(b) ASCII (American Standard Code for
Information Interchange)
widely used in Communication and microcomputer.
7 bits (126 characters)
MSB parity: bit for checking
purpose.
A partial Character List for ASCII
Character
ASCII
73
74
ARARNE25.......ORENAJAR
This table will be given in both papers in the HKCES Characters. aneshown.
You just have to know how to use it.
As are represented by seven bits.:
165 bit pattern > {11101010003
parity ASCII 66 bit pattern is 1000010 B: ASCII = * ajsebattern is 1000000
Excess-16 aresresentation exponent.
the
1.0.0.0.0.1.0
wulf 5. bits nekarteux for then representations are
01.0
oxponent
00000
00001
00010
negative exponent.
The ASOL
:blt Linery
paint
10000
Zero exponent
point representation may
1.1-101
dependent. Different
positive exponent
11110
different formats.
11111
Exercise: Convert
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LOTUS 123
DBASED O
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into ASCII code.
Character
ASCIE
98 99
100
1,011
102
103
104
105
106
107
:108
109
110
111
112
113
114
115
116
117
118.
119
120
121
122
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