Section 7.3
Review Questions
Control Points
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Define control point.
answer...
a wire that causes things to happen in the computer
-
In the figure below, circle or indicate some control wires and
then, using a different color or some other manner, point out a few
data wires.
answer...
control point wires have names and are depicted as short wires (though
they aren't really). Data wires are the long wires between components.
-
What is the name of the combinational circuit that acts as a traffic
cop, directing several different roads that converge to the same
place? In this analogy, roads are wires and the "same place" refers to
the registers.
answer...
multiplexor (or mux)
-
Which of the 8 combinations of the F control wires correspond to actual
instructions in the CSC-1's instruction set?
answer...
7
-
Why can't the CSC-1 handle circular and arithmetic shifts, since it already
handles right and left logical shifts?
answer...
we just haven't built in these shifting instructions and the shifter
circuit that we have isn't smart enough to do these other shifts.
-
Which component generates the C, N, Z and V wires?
answer...
the ALU
-
Which two control wires control main memory?
answer...
WR and MA
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Who or what decides when and which control wires get turned on and off?
answer...
the instruction code
-
Suppose that we wanted to be able to funnel the PC's output into the A
register. What would this mean for A's multiplexor?
answer...
it would have 5 data inputs and hence 3 mux address control wires
(mux2, mux1 and mux0)
-
For each of the F codes below, write what function the ALU computes.
F2 F1 F0
------------------------------
1 1 1 ______________
0 1 0 ______________
0 0 1 ______________
0 1 1 ______________
1 0 1 ______________
0 0 0 ______________
1 1 0 ______________
1 0 0 ______________
answer...
F2 F1 F0
------------------------------
1 1 1 __not used____
0 1 0 __A AND TMP___
0 0 1 __TMP_________
0 1 1 __A OR TMP____
1 0 1 __A + TMP_____
0 0 0 __A___________
1 1 0 __A - TMP_____
1 0 0 __NOT A_______