Figure 9-4(a) shows how four 74ALS138s and an INVERTER can be arranged to function as a 1-of-32 decoder. The decoders are labeled Z₁ to Z₄ for easy reference, and the eight outputs from each one are combined into 32 outputs. Z₁’s outputs are O̅₀ to O̅₇; Z₂’s outputs O̅₀ to O̅₇ are renamed O̅₈ to O̅₁₅, respectively; Z_3’s outputs are renamed O̅₁₆ to O̅₂₃; and Z₄’s are renamed O̅₂₄ to O̅₃₁. A five-bit input code A₄A₃A₂A₁A₀ will activate only one of these 32 outputs for each of the 32 possible input codes.

(a) Which output will be activated for A₄A₃A₂A₁A₀ = 01101?

(b) What range of input codes will activate the Z₄ chip?

(c) Create a megafunction circuit in Quartus that will implement a 1-of-32 decoder with active-HIGH outputs.

Figure 9-4(a)

Transcribed Image Text:

A₂ A3 A4 (MSB) A₂A₁A₂ Ōo 00 123 --- E 74ALS138 Z₁ 0 1 2 3 4 5 6 7 +5 V 07 123 A0 A₁ A₂ 74ALS138 Z₂ 0 1 2 3 4 5 6 7 1000 08 E 123 A₂ A₁ A₂ 74ALS138 Z3 0 1 2 3 4 5 6 7 5000 015 016- (a) E A₂A₁A₂ 123 023 024 E 74ALS138 Z4 0 1 2 3 4 5 6 7 031