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I hope this is the correct section to ask. Since the ALU is part of a processor which is a part of computer, I think it's not too bad.

Given is an n-Bit-ALU with OM (=operating mode), control vector S=(S_0, S_1, S_2, S_3) and 2 entrace vectors A=(A_n-1, A_n-2, ..., A_o), B=(B_n-1, B_n-2,..., B_o). Extrance vector Q = (Q_n-1, Q_n-2, ..., Q_0).

The switching function of the ALU is:

enter image description here

Proof that Q = B if S = 1001 and OM = 1

S= 1001 means S_0 = 1, S_1 = 0, S_2 = 0, S_3 = 1

OM operating mode describes if the operation is arithmetic or logic. OM = 1 --> logic operation (AND, OR, NOR...) if OM = 0 its an arithmetic operation (addition, sub, mul...)

So if we put that into this term we have:

enter image description here

But I don't know what to do now to get Q = B.

I get to:

enter image description here

No idea how to continue or if it's correct at all.

I hope someone can help me here please I got no one else to ask that. This is no homework. It's a task from an old exam (2014) but sadly there were no solutions and now I'm trying to solve all tasks. And these ones I don't understand, I try solve as much as I can and post here like this one.

rpbudd
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  • What is C_i-1? It appeared somewhat fast for my slow thinking.. also symbol "V" in this case is still logical OR, as I recall it's usage from my uni? Then (1 V ..anything ) will end as 1? I'm quite lost, sorry. Would need some explanation to recall what is what exactly. – Ped7g Sep 09 '16 at 15:34
  • C_i-1 the -1 confused me too here but C_i means carry. Symvol "V" means OR, yes. (1 V anything) will end as 1 I believe but not sure about that : / – rpbudd Sep 09 '16 at 15:47
  • But im pretty sure (1 AND anything) = anything. OR should be the opposite, so it should be right our thought. – rpbudd Sep 09 '16 at 15:52
  • Ok, then I get it even less, the OM is constant 1? What is then the triple `=`, I though it's some sort of equivalence, but then I end with yours `Q_i = 1`, which is no way equal to B_i obviously, thus we did prove Q != B (only for case where B is full of ones). – Ped7g Sep 09 '16 at 15:55
  • OM operating mode describes if the operation is arithmetic or logic. OM = 1 --> logic operation (AND, OR, NOR...) if OM = 0 its an arithmetic operation (addition, sub, mul...) – rpbudd Sep 09 '16 at 15:58
  • Maybe the task is complete bullsh...? I don't see a way getting this Q = B – rpbudd Sep 09 '16 at 16:00
  • I'm voting to close this question as off-topic because it's about a theoretical ALU design and not about programming. – Ross Ridge Sep 09 '16 at 16:04
  • So where would you suggest asking this question? – rpbudd Sep 09 '16 at 16:08
  • Do you a source? For example, the website or book where you found this? – Margaret Bloom Sep 09 '16 at 16:40
  • http://www.directupload.net/file/d/3709/4qywjyna_pdf.htm "Aufgabe 3" – rpbudd Sep 09 '16 at 16:44
  • By the way, why asking for source if you don't contribute anything anyway? – rpbudd Sep 11 '16 at 11:50

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