Lecture 6
Excess Notation
Excess Notation
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Excess 8 notation indicates that the value for
zero is the bit pattern for 8, that is 1000
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The bit patterns are 4 bits long
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Positive numbers are above it in order and
negative numbers are below it in order.
Figure 1.24 An excess eight
conversion table
Excess Notation (continue)
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That is the zero point for Excess 128 notation is
128; the zero point for excess 64 notation is 64; and so
forth.
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For example, let's say we want to determine the pattern
for 15 in Excess 128 notation.

The decimal number would be 128 + 15, or
143. Therefore, the bit pattern would be 10001111.
Excess Notation Formulas
Example1

A computer stores decimal integer values in 8
bits, using excess-128 notation. How would the
decimal value -60 stored?
Solution:
stored number = -60 + 128
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= 6810 (10001002)
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Example 2

The binary number, 0101 1101, is in excess-128
notation. What is the number in decimal?

Solution:
0101 1101 = 0*128 + 64 + 0*32 + 16 +8 + 4 +
0*2 + 1
= 93 in excess-128
actual number = 93 – 128 = -35
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