Hardware Reference
In-Depth Information
Figure 8.38
a) Present a state transition diagram for an FSM capable of producing the signal of
i gure 8.37a. Estimate the number of DFFs needed to build your complete circuit for
T
= 3 clock cycles and sequential encoding.
b) Do the same for the signal of i gure 8.37b. Assume sequential encoding and
T
1
= 3
and
T
2
= 5 clock cycles.
Exercise 8.18: Triggered Circuits #3
Figure 8.38a shows a two-machine arrangement for the implementation of an edge-
detecting triggered circuit. We want to use this arrangement to implement a circuit
that generates the signal of i gure 8.24a. A solution for that case was already seen in
i gure 8.24b, using a single machine. The advantage of the approach discussed here is
that the timer can be zeroed every time the machine changes its state; hence, contrary
to i gure 8.24b, strategy #1 (section 8.5.2) can be applied without exceptions. In i gure
8.38a, FSM1 is a one-shot circuit (discussed in section 5.4.3) that converts
x
into a
short pulse (internal signal
i
), from which FSM2 must produce the actual output signal,
y
, as illustrated in i gure 8.38b. Present two state transitions diagrams (one for each
machine) to solve this problem with the timer allowed to be zeroed at every state
transition. Can the timer control strategy #2 also be employed in your FSMs?
Exercise 8.19: Pulse Shifter
This exercise concerns the pulse shifter introduced in section 8.11.9.
a) Draw a state transition diagram and present an illustrative timing diagram for an
FSM capable of producing a signal similar to that in i gure 8.25b, but knowing that
x
(still synchronous) now lasts exactly one clock period.
b) How many l ip-l ops are needed to build your circuit, for
T
shift
= 16
T
clk
, using sequen-
tial encoding for the FSM?
Exercise 8.20: Synchronous Pulse Stretcher #1
This exercise concerns the synchronous version of a pulse stretcher whose behavior
was depicted in i gure 8.27b.
a) If the falling edge of signal 2 is beyond the falling edge of (sync)
y
, will the solution
presented in i gure 8.28a still produce the same result? If not, modify it to accom-
modate this situation as well.
