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combinational circuits

Discussion in 'General Electronics Chat' started by vead, Jun 27, 2014.

Nov 24, 2011
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2. djsfantasi AAC Fanatic!

Apr 11, 2010
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D0 through D3 are individual outputs. The input to the decoder is switched to one of the four outputs, based on the values of the select lines S0 and S1. For example, if S0=1 and S1=1, then D3 is selected ('11b'=3).

In the case of the linked examples, there is no input but the selected output is set to 1 (and the others are set to 0), based on the select lines as described above.

3. MrAl AAC Fanatic!

Jun 17, 2014
6,402
1,388
Hi,

You can write the boolean expression for each output.

For example, D0=A0'*A1'

4. DerStrom8 Well-Known Member

Feb 20, 2011
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1,355
When working with logic gates I find it useful to write the values at the output. For example, if I have inputs A and B going into a NAND gate, then just after the NAND gate I write (A*B)!, and use that for the input to the next gate. Writing the values of the gates starting from the inputs and working towards the output really simplifies the process of determining what you get at the output.

Nov 24, 2011
712
11
so look third row in table (demultiplexer) A=0

D0= 00*01=1

but its wrong

6. MrAl AAC Fanatic!

Jun 17, 2014
6,402
1,388

Hi,

I am sorry but i dont understand what you are trying to say.

What i see is under the column for D0 i see a zero when A1=1 and A0=0, which looks correct to me because 1 times 0 (or alternately 1 AND 0) equals 0 (zero) so that looks correct.

D0=A1'*A0'
D1=A1'*A0
D2=A1*A0'
D3=A1*A0

These statements show when the associated output (D0 through D3) is HIGH (equivalent to a '1').

Note the following:
0*0=0
0*1=0
1*0=0
1*1=1

Does this make any more sense?