EECS 270, Fall 2009, Lecture 5
Page
1
of
6
I.
Announcements
•
We are changing things up.
Dr. Sakallah will be teaching the next 3 lectures.
II. Some additional stuff
A few catchup things about 2’s complement numbers.
First
of all, let’s consider what happens when we add 2’s
complement numbers and we get an overflow.
Consider the 4bit case where we add 7+1.
The result will
be 8 (see picture).
If we then subtract 2 we’ll get back to 6!
Question:
What is ((4+4)+4)6 when we do the math as a 4bit 2’s complement number?
Second
, in order to find the complement of a 2’s complement number (change the sign) all you need to do
is complement each bit (0s go to 1s and 1s go to 0s) and then add one. Try it with 0101 and with 1011.
In
what case doesn’t this work?
Tristate devices
III.
The day of problem solving
As our class schedule indicates, today we are going to spend most of the day working sample problems.
A.
Using the rules of logic, convert (A+B)’*(D*C)’ into sumofproducts form.
Provide the name of
the rule used for each step.
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 Spring '11
 david
 Input device, complement number

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