These questions refer to Figure 18 19 (p 428) in the text which is reproduced be

Question

These questions refer to Figure 18 19 (p 428) in the text which is reproduced below (20 points. 6 67 points each for 4 a. 4 b and 4 c) What is the purpose of the circuit? What happens to the LEDs when the Output Enable line is low (0)? What input bit pattern do I need to light the LED attached to pm 10 (output ) of the integrated circuit? I am asking for the states of the inputs labeled Select Bit 0. Select Bit 1 and Select Bit 0 Assume the Output Enable line is high (1) Note when an output is addressed, it goes low (0). When an output is not addressed or the chip is not selected then the output(s) is high (1)

Explanation / Answer

1)Its a decoder circuit and decodes the 3 input lines to 23 ouput lines as shown in the diagram.

2) The outputs are active low and hence when the output enable goes low,the output go low and hence LEDs become reverse biased,remain in off-mode or LEDs doesnt glow.

3)consider Y15 for a 111 sequence and Y7 for a 000 sequence and hence for LED as pin 10 to glow,the input sequence must be 010 

=> A=0,B=1,C=0 ; 

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