A technician tests the circuit of Figure 9-4 as described in Example 9-7, and she obtains the following results: all of the outputs work except O̅₁₆ to O̅₁₉ and O̅₂₄ to O̅₂₇, which are permanently HIGH. What is the most probable circuit fault?

Data from Example 9-7

A technician tests the circuit of Figure 9-4 by using a set of switches to apply the input code at A₄ through A₀. She runs through each possible input code and checks the corresponding decoder output to see if it is activated. She observes that all of the odd-numbered outputs respond correctly, but all of the even-numbered outputs fail to respond when their code is applied. What are the most probable faults?

Figure 9-4

Transcribed Image Text:

Ao A₁ A₂ Ag A₁ (MSB) AA₁A₂ 00 123 74ALS138 Z₁ mb E 160 +5 V 00 123 Ō, A₂ A₁ A₂ 74ALS138 Z₂ 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 E 123 A₁ A₁ A₂ 74ALS138 Z3 0 1 2 3 4 5 6 7 015 016 (a) E A₂A₁A₂ 123 023 024 E 74ALS138 Z₂ 0 1 2 3 4 5 6 7 031 1 of 32 da ta [4..0] (b) eqo eq1 eq2 eq3 eq4 eq5 eq6 eq7 eq8 eq9 eq10 eq11 eq12 eq13 eq14 eq15 eq16 eq17 eq18 eq19 eq20 eq21 eq22 eq23 eq24 eq25 eq26 eq27 eq28 eq29 eq30 eq31 inst2