While testing the circuit of Figure 9-16, a technician finds that every odd-numbered key results in the correct digit being entered, but every even-numbered key results in the wrong digit being entered as follows: the 0 key causes a 1 to be entered, the 2 key causes a 3 to be entered, the 4 key causes a 5 to be entered, and so on. Consider each of the following faults as possible causes of the malfunction. For each one, explain why it can or cannot be the actual cause.

(a) There is an open connection from the output of the LSB inverter to the D inputs of the FFs.

(b) The D input of flip-flop Q₈ is internally shorted to V_CC.

(c) A solder bridge is shorting O̅₀ to ground.

Figure 9-16

Transcribed Image Text:

Digit kays +5V 1 kn For switch bounce T OS Q = 20 ms Pull-up resistor for each input 74LS147 decimal- to-BCD encoder ->CLK CLEAR 1 k MSB ā₂ CLA +5 V LSB X J CLK CLA To CLR inputs of Qo-Q₁1 PRE CLK D D D D Ond CLK D D D D D To decoder/drivers and displays Q₁₁ D CLK 0₂ CLK 0₂ CLK CLK CLK Q₁ CLK 0₂ CLK Q₂ CLK D 0₂ CLK BCD code for MSD Second MSD LSD