# Shift Through on a circuit?

Discussion in 'The Projects Forum' started by hokxj, Apr 14, 2010.

1. ### hokxj Thread Starter New Member

Apr 14, 2010
1
0
Hi, so I'm doing an assignment and we need to build a 4 bit 4 function ALU.
the 4 functions are:

S1 S2 OUTPUT
0 0 Shift A Through (X = A)
0 1 Logical AND (X = A AND B)
1 0 Logical XOR (X = A XOR B)
1 1 Full adder (X = A + B)

I've attached a picture of what my ALU looks like now, before any shifts.

I don't understand the term shift through? I looked through my lecture notes and they don't explain it. From what i understand, to make a shift register that can shift bits left or right, you need flip flops, but I'm completely at loss with shift through.

Any help would be greatly appreciated,
thanks

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2. ### rjenkins AAC Fanatic!

Nov 6, 2005
1,015
69
Shift can just mean Move.

Your function table says it: X = A

In a built-up ALU it may be done by something like X = A XOR 0 (zero)
or X = A AND 1111; whatever is the easiest logic path to move A to X unchanged.