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1
EEE 410 – Microprocessors I
Fall
05/06 – Lecture Notes # 13
Outline of the Lecture
•
Signed Numbers and Signed Number Operations
S
IGNED
N
UMBER
A
RITHMETIC
O
PERATIONS
¾
Until now we have seen unsigned numbers where entire 8bit or 16bit operand was used for the
magnitude.
¾
In order to represent positive and negative numbers signed numbers have been introduced. The
representation of signed numbers:
♦
The MSB is set aside for the
sign
(+ or –) and the rest of the bits are used
for the magnitude.
♦
The sign is represented by 0 for positive (+) numbers and 1 for (–)
negative numbers.
Signed byte operands:
D7
D6
D5
D4
D3
D2
D1
D0
sign
If D7=0
the operand is positive
If D7=1
it is negative.
Positive Numbers:
The range of positive numbers that can be represented as a signed byte operand is
0 to +127.
Ex:
0
0000 0000
Note:
If a positive number is larger than
+1
0000 0001
+127, a wordsize operand must be
+5
0000 0101
used.
::
:::::::::::::::
+127
0111 1111
Negative Numbers:
For negative signed numbers D7=1, but the magnitude operand is represented in 2’s complement.
Although the assembler does the conversion, it is important to understand how the conversion works.
To convert to negative number representation (2’s complement) follow the steps:
1.
Write the magnitude of the number in 8bit binary (no sign)
2.
Invert each bit
3.
Add 1 to it
Ex: Show how the computer would represent –5
1.
0000 0101
5 in 8bit binary
2.
1111 1010
invert each bit
3.
1111 1011
add 1 (hex = FBH)
This is the signed number representation of –5 in 2’s complement.
Ex: Show how the computer would represent –34H
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This note was uploaded on 05/26/2011 for the course EEE 410 taught by Professor Hasandemirel during the Spring '10 term at Eastern Mediterranean University.
 Spring '10
 HASANDEMIREL
 Microprocessor

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