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You're reading from  Modern Computer Architecture and Organization – Second Edition - Second Edition

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Published inMay 2022
PublisherPackt
ISBN-139781803234519
Edition2nd Edition
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Jim Ledin
Jim Ledin
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Jim Ledin

Jim Ledin is the CEO of Ledin Engineering, Inc. Jim is an expert in embedded software and hardware design and testing. He is also an expert in system cybersecurity assessment and penetration testing. He has a B.S. degree in aerospace engineering from Iowa State University and an M.S. degree in electrical and computer engineering from the Georgia Institute of Technology. Jim is a registered professional electrical engineer in California, a Certified Information System Security Professional (CISSP), a Certified Ethical Hacker (CEH), and a Certified Penetration Tester (CPT).
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Chapter 3: Processor Elements

Exercise 1

Consider the addition of two signed 8-bit numbers (that is, numbers in the range -128 to +127) where one operand is positive and the other is negative. Is there any pair of 8-bit numbers of different signs that, when added together, will exceed the range -128 to +127? This would constitute a signed overflow. Note: we’re only looking at addition here because, as we’ve seen, subtraction in the 6502 architecture is the same as addition with the right operand’s bits inverted.

Answer

The range of the positive (or non-negative) numbers is 0 to 127. The range of negative numbers is -128 to -1. It is only necessary to consider the extremes of each of these ranges to cover all possibilities:

Sum

Result

0 + -128

-128

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Modern Computer Architecture and Organization – Second Edition - Second Edition
Published in: May 2022Publisher: PacktISBN-13: 9781803234519

Author (1)

author image
Jim Ledin

Jim Ledin is the CEO of Ledin Engineering, Inc. Jim is an expert in embedded software and hardware design and testing. He is also an expert in system cybersecurity assessment and penetration testing. He has a B.S. degree in aerospace engineering from Iowa State University and an M.S. degree in electrical and computer engineering from the Georgia Institute of Technology. Jim is a registered professional electrical engineer in California, a Certified Information System Security Professional (CISSP), a Certified Ethical Hacker (CEH), and a Certified Penetration Tester (CPT).
Read more about Jim Ledin