MC48 Homework 3 (Fall 1996)
Due: October 3, 1996
Note that I plan to do at least exercise 4.33, and probably also
exercise 4.31 and/or part or all of 4.34 in class. Their inclusion in
the homework assignment just means that you need to clearly write up
what we've done in a more casual oral style in class.
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Do exercise 4.9 on page 304.
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Do exercise 4.31 on page 308; the reference to page 202 should be to
pages 224-226.
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Do exercise 4.32 on page 308.
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Do exercise 4.33 on page 308. Where the problem statement refers to
page 200, that should be page 223. In this and the following two
exercises, remember that as many equations as necessary can be
calculated simultaneously, so long as their inputs are all
available. For example, initially all the ai
and bi inputs are available at time 0, and so is
c0, so during the first time unit (T), all of the pi and gi
can simultaneously be calculated, so that at time T, they are now
all available, and all the equations using them can simultaneously be
calculated. Here, in concise form, are the ground rules:
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At time 0, all ai and bi inputs are
available. So is c0, the carry in to the overall adder.
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If
at any particular time, t, the last of the values used on the right
hand side of an equation becomes available, then the value of the
left-hand side will become available at time t+T if the equation
contains only AND or only OR, and at time t+2T if the equation
contains both AND and OR. It is irrelevant what else is going on
concurrently.
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Whichever output bit becomes available last, whether it is one of the
sum bits or the carry out bit
(cn in an n-bit adder), signals the
end of the computation: when that last output is available, the
computation is over. The completion time is the total
elapsed time, since we started at time 0.
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Do exercise 4.34 from page 263. The reference to page 202 should be
to pages 225-226. The three options you are to compare
can be restated as follows:
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Sixteen one-bit adders hooked together in ripple-carry fashion.
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Four four-bit adders hooked together in ripple-carry fashion. Inside
each of the four-bit adders, however, the carry lookahead is used.
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Four four-bit adders hooked together in carry lookahead fashion. As in
the previous option, carry lookahead is used within each of the
four-bit adders as well.
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Do exercise 4.35 from page 308. The four options to compare can be
restated as follows:
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Sixty-four one-bit adders hooked together in ripple-carry fashion.
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Sixteen four-bit adders hooked together in ripple-carry fashion. Inside
each of the four-bit adders, however, the carry lookahead is used.
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Four sixteen-bit adders hooked together in ripple-carry fashion. Each
of the sixteen-bit adders is built as in
option 3 of the prior exercise.
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Four sixteen-bit adders hooked together in carry lookahead fashion. As in
the previous option, the sixteen-bit adders are built as in
option 3 of the prior exercise.
Instructor: Max Hailperin