1. Instructor: Alexander Stoytchev
CprE 281: Digital Logic
Instructor: Alexander Stoytchev

2. Intro to Verilog CprE 281: Digital Logic
Iowa State University, Ames, IA
Copyright © Alexander Stoytchev

3. Administrative Stuff HW4 is out It is due on Monday Sep 22 @ 4pm.
Please write clearly on the first page (in BLOCK CAPITAL letters) the following three things:
Your First and Last Name
Your Student ID Number
Your Lab Section Letter
Also, please
Staple your pages
Use Letter-sized sheets

4. Quick Review

5. NAND followed by NOT = ANDx 1 2 × x 1 2 × x 1 2 × x 1 x 2 x1 x2 f 1 f 1 x1 x2 f 1

6. DeMorgan’s Theorem

7. DeMorgan’s Theorem x x x y × =
x + y y y

8. Sum-Of-Products x 1 2 3 4

9. Sum-Of-Products
AND x 1 2 3 4 OR
AND

10. Sum-Of-Products
AND x 1 2 3 4 OR
AND x 1 2 × 3 4 +

11. Sum-Of-Products
AND x 1 2 3 4 OR
AND
AND x 1 2 × 3 4 + OR
AND

12. Sum-Of-Products
AND x 1 2 3 4 OR
AND x 1 2 × 3 4 +

13. Sum-Of-Products
AND x 1 2 3 4 OR
AND
NAND x 1 2 × 3 4 +

14. Sum-Of-Products AND OR AND x + 1 2 3 4 × × × × x x x x x x x x 1 2 1 2

15. Sum-Of-Products x x x x x x x x x x x x x x x 1 1 2 2 3 3 4 4 5 5 1 2

16. 2-1 Multiplexer (Definition)
Has two inputs: x1 and x2
Also has another input line s
If s=0, then the output is equal to x1
If s=1, then the output is equal to x2

17. Graphical Symbol for a 2-1 Multiplexer
[ Figure 2.33c from the textbook ]

18. Let’s Derive the SOP form
s x1 x2
s x1 x2
s x1 x2
s x1 x2
f (s, x1, x2) =
s x1 x2 +

19. Let’s simplify this expression
f (s, x1, x2) =
s x1 x2 +
f (s, x1, x2) =
s x1 (x2 + x2)
s (x1 +x1 )x2 +
f (s, x1, x2) =
s x1
s x2 +

20. Circuit for 2-1 Multiplexers
(c) Graphical symbol
(b) Circuit
[ Figure 2.33b-c from the textbook ]

21. Analogy: Railroad Switch

22. Analogy: Railroad Switchx2 x1
select f

23. Analogy: Railroad Switchx2 x1
select f
This is not a perfect analogy because the trains can go in either direction,
while the multiplexer would only allow them to go from top to bottom.

24. More Compact Truth-Table Representation1
(a)
Truth
table s x1 x2
f (s, x1, x2) 1
f (s, x1, x2) s x1 x2
[ Figure 2.33 from the textbook ]

25. 4-1 Multiplexer (Definition)
Has four inputs: w0 , w1, w2, w3
Also has two select lines: s1 and s0
If s1=0 and s0=0, then the output f is equal to w0
If s1=0 and s0=1, then the output f is equal to w1
If s1=1 and s0=0, then the output f is equal to w2
If s1=1 and s0=1, then the output f is equal to w3
We’ll talk more about this when we get
to chapter 4, but here is a quick preview.

26. Graphical Symbol and Truth Table
[ Figure 4.2a-b from the textbook ]

27. The long-form truth table[

28. 4-1 Multiplexer (SOP circuit)
[ Figure 4.2c from the textbook ]

29. Using three 2-to-1 multiplexers to build one 4-to-1 multiplexerw w 1 1 f 1 w 2 w 3 1
[ Figure 4.3 from the textbook ]

30. Analogy: Railroad Switches

31. Analogy: Railroad Switchesf

32. Analogy: Railroad Switches
these two
switches are
controlled
together s1 f

33. Using three 2-to-1 multiplexers to build one 4-to-1 multiplexer

34. Using three 2-to-1 multiplexers to build one 4-to-1 multiplexerw0 w1 s1 f s0 w2 w3

35. That is different from the SOP form of the 4-1 multiplexer shown below, which uses less gates

36. 16-1 Multiplexer s f w [ Figure 4.4 from the textbook ] 1 3 4 2 7 8 113 4 7 12 15 2 f
[ Figure 4.4 from the textbook ]

37. [http://upload. wikimedia. org/wikipedia/commons/2/26/SunsetTracksCrop[

38. 7-Segment Display Example

39. Display of numbers
[ Figure 2.34 from the textbook ]

40. Display of numbers

41. Display of numbers a = s0 c = s1 e = s0 g = s1 s0 f = s1 s0 d = s0

42. Intro to Verilog

43. History Created in 1983/1984 Verilog-95 (IEEE standard 1364-1995)
SystemVerilog
SystemVerilog 2009 (IEEE Standard ).

44. HDL
Hardware Description Language
Verilog HDL
VHDL

45. Verilog HDL != VHDL These are two different Languages!
Verilog is closer to C
VHDL is closer to Ada

46. [ Figure 2.35 from the textbook ]

47. “Hello World” in Verilog[

48. The Three Basic Logic Gatesx 1 2 × x 1 2 + x
NOT gate
AND gate
OR gate
[ Figure 2.8 from the textbook ]

49. How to specify a NOT gate in Verilogx
NOT gate

50. How to specify a NOT gate in Verilog
we’ll use the letter y for the output x y
NOT gate

51. How to specify a NOT gate in Verilogx y
not (y, x)
NOT gate
Verilog code

52. How to specify an AND gate in Verilogx 1 2 × f=
and (f, x1, x2)
AND gate
Verilog code

53. How to specify an OR gate in Verilogx 1 2 + f=
or (f, x1, x2)
OR gate
Verilog code

54. 2-1 Multiplexer
[ Figure 2.36 from the textbook ]

55. Verilog Code for a 2-1 Multiplexer
[ Figure 2.36 from the textbook ]
[ Figure 2.37 from the textbook ]

56. Verilog Code for a 2-1 Multiplexer
[ Figure 2.36 from the textbook ]
[ Figure 2.40 from the textbook ]

57. Verilog Code for a 2-1 Multiplexer
[ Figure 2.36 from the textbook ]
[ Figure 2.42 from the textbook ]

58. Verilog Code for a 2-1 Multiplexer
[ Figure 2.36 from the textbook ]
[ Figure 2.43 from the textbook ]

59. Another Example

60. Let’s Write the Code for This Circuit
[ Figure 2.39 from the textbook ]

61. Let’s Write the Code for This Circuit
module example2 (x1, x2, x3, x4, f, g, h);
input x1, x2, x3, x4;
output f, g, h;
and (z1, x1, x3);
and (z2, x2, x4);
or (g, z1, z2);
or (z3, x1, ~x3);
or (z4, ~x2, x4);
and (h, z3, z4);
or (f, g, h);
endmodule 
[ Figure 2.39 from the textbook ]
[ Figure 2.38 from the textbook ]

62. Let’s Write the Code for This Circuit
module example4 (x1, x2, x3, x4, f, g, h);
input x1, x2, x3, x4;
output f, g, h;
assign g = (x1 & x3) | (x2 & x4);
assign h = (x1 | ~x3) & (~x2 | x4);
assign f = g | h;
endmodule
[ Figure 2.39 from the textbook ]
[ Figure 2.41 from the textbook ]

63. Yet Another Example

64. A logic circuit with two modules
[ Figure 2.44 from the textbook ]

65. The adder module
[ Figure 2.12 from the textbook ]

66. The adder module
[ Figure 2.45 from the textbook ]

67. The display module a = s0 c = s1 e = s0 g = s1 s0 f = s1 s0 d = s0
b = 1

68. The display module a = s0 b = 1 c = s1 d = s0 e = s0 f = s1 s0
g = s1 s0
[ Figure 2.46 from the textbook ]

69. Putting it all together

70. Questions?

71. THE END