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Unformatted text preview: PART A  Digital QUESTION 1 Suppose the decimal integer values ﬂour 0 to 255 are to be transmitted. (a) How many lines will be needed if parallel representation is used?
(1)) How many lines will be needed if serial representation is used? A: (a) 8 (b) 1 QUESTION 2 (a) Convert the following numbers to decimal; (show all working)
1010101 1 1)
5A 11
1000010110001BCD (b) Convert the following numbers to binary; (show all working)
A5 h
139 d
000110010101 BCD A: (a) 171, 90, Error BCD not possible (b) 10100101, 10001011,195
noooau QUESTION 3 One of DeMorgans’s Theorems is that Z + E = FB—
Prove that the theorem also works for th‘reee variables. That is, prove Z+1§+ZF=ABC a.“ A:2+§+E= 3+5
LetDjAB .'.=,D+¥C‘ ‘ =55 =ABC Q.E.D. (2Marks)
(2Marks) (3Marks) (3Marks) QUESTION 4
(a) Write the output expression for ﬁgure 1. ( 2 Marks)
(b) simplify the output expression with boolean theorems. ( 3 Marks ) A:(a)ZE+ABC+AE+ABE=F
(b)F=Z+E+ABC+Z+C+AB'C“
As C+E=I 3F=i F=0 QUESTION 5
A NC lathe employsa system for monitoring the lathes safety by monitoring sliding door, oil coolent
and rotation status. These operate as follows: ”
Door = 1 when sliding door is open.
Oil = 1 when oil is present.
Rotation Status = 1 when work piece is rotating
Figure 2 shows the logic circuit that controls a warning light for certain combinations of safety
conditions. Assume that a HIGH at output W activates the warning light.
(a) Determine what conditions will give a warning to the operator. ( 3 Marks )
(b) Change the circuit to one using all NAND gates. ( 2 Marks ) QUESTION 6
An edgetriggered D ﬂipﬂop and a T ﬂipﬂop aren wired up as in ﬁgure 3.
(a) Assume that Q = 0 initially, determine the Q waveform. ( 2 Marks ) (b) Describe the operation of this circuit. ( 3 Marks) 8KHz Figure 3 A: (a) Both devices set up to toggle so the ﬁnal Q output will be a square wave of 21012
(b) This is a divide by 4 circuit QUESTION 7
Analyse the following circuit and draw its truth table.
Is it ﬁmctionally the same as a NAND gate SR latch?
( 5 Marks) Yes, it is functionally equivalent ...
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 Spring '08
 Trinh
 Logic gate, following numbers, decimal integer values, NAND gate SR

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