Hardware Reference
In-Depth Information
Exercise 5.4: Truly Complementary Transition Conditions
In section 1.5 the importance of having the state transition diagram neither under- nor
overspecii ed was discussed. What happens if, in the garage door controller of i gure
5.9c, the condition
sen1
= '0' is removed from the
opening1
-
opening2
transition, or the
condition
sen2
= '0' is removed from the
closing1
-
closing2
transition?
Exercise 5.5: One-Shot Circuits Analysis
a) It is said in section 5.4.3 that the solution in i gure 5.7d is inferior to that in i gure
5.7c. Why? (Suggestion: i ll in the last two plots of i gure 5.16 and you will see the
answer.)
b) Is reset indispensable in these two solutions?
c) In order to answer the question posed at the end of section 5.4.3, solve exercise 3.3
if not done yet.
Exercise 5.6: Two-Signal-Triggered One-Shot Circuit
Figure 5.17 shows an illustrative timing diagram for a one-shot circuit that is not trig-
gered by a single signal but rather by a pair of signals. The triggering condition is the
following: the one-shot pulse (in
y
) must be generated if the control signal
x
lasts at
least as long as the
dv
pulse (this is obviously checked only at positive clock transi-
tions). Note in the i gure that only the i rst pulse of
x
fuli lls this requirement, so the
one-clock-period pulse in
y
has to be produced only in that case. Draw the state transi-
tion diagram for a state machine capable of implementing this circuit.
Exercise 5.7: Arbiter
Arbiters are used to manage access to shared resources. An example is depicted
in i gure 5.18, which shows three peripherals (P1 to P3) that use a common bus
Figure 5.16
Figure 5.17