Hardware Reference
In-Depth Information
distributed, so some type of counter/adder can be used to build it. Say that the circuit
must generate values from 0 to 99, incremented (when
up
= '1') or decremented (when
dn
= '1') in steps of size 1.
a) Make a sketch for this circuit, detailing especially the connections of the two push-
buttons (feel free to add other contacts to the pushbuttons if you consider it neces-
sary). How many debouncers are needed?
b) How many l ip-l ops are needed to build the entire circuit of i gure 8.19a based on
your sketch above? If any debouncer is needed, consider 1 ms for the debouncing
interval and
f
clk
= 50 MHz.
Exercise 8.13: Traffi c Light Controller
The questions below refer to the trafi c light controller of i gure 8.20c.
a) Explain why either strategy #1 or #2 (section 8.5) can be used to implement the
timer in this machine.
b) Is a reset signal needed? Explain. (Suggestion: Review sections 3.8 and 3.9.)
c) Which inputs are asynchronous? (Suggestion: Review section 2.3.)
d) If debouncers are included in the asynchronous inputs, are synchronizers needed?
e) If debouncers are not used, are synchronizers indispensable in this application?
f) Redraw the state transition diagram including in it the following feature: Instead of
having the yellow lights in both directions statically on while in standby mode, make
them blink continuously (with a 0.5 Hz frequency) in that mode.
g) The number of DFFs needed to build the FSM after the feature above is included is
still that determined in section 8.11.5? Explain.
Exercise 8.14: Car Alarm
The questions below refer to the car alarm of i gure 8.21c. Assume that the chirps must
last 0.3 s and
f
clk
= 50 MHz.
a) Explain why both strategies #1 and #2 (section 8.5) are appropriate to imple-
ment the timer in this machine. What are the advantages and disadvantages of
each one?
b) How many DFFs are needed to build that circuit with sequential encoding for the
machine states? And with one-hot encoding?
c) Is a reset signal needed? Explain. (Suggestion: Review sections 3.8 and 3.9.)
d) Which inputs are asynchronous? (Suggestion: Review section 2.3.)
e) If debouncers are included in the asynchronous inputs, are synchronizers needed?
f) If debouncers are not used, are synchronizers indispensable in this application?
Exercise 8.15: Password Detector
The questions below refer to the password detector of i gure 8.22c.
