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# y<=(a and b) xor (not b and c);What's the output of this VHDL code?

#### oslon

##### New Member

This is a no-answer problem and I am self studying via online tutorials w/o real teachers. Anyone can verify this?

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The VHDL code you provided represents a logical expression. To determine its output, we need to evaluate it based on the values of the variables aa, bb, and cc.

Here's the evaluation:

1. If a=0a=0, b=0b=0, and c=0c=0:
• (a(a and b)=(0b)=(0 and 0)=00)=0
• (notb(notb and c)=(not0c)=(not0 and 0)=00)=0
• (a(a and b)b) xor (notb(notb and c)=0c)=0 xor 0=00=0
2. If a=1a=1, b=0b=0, and c=1c=1:
• (a(a and b)=(1b)=(1 and 0)=00)=0
• (notb(notb and c)=(not0c)=(not0 and 1)=11)=1
• (a(a and b)b) xor (notb(notb and c)=0c)=0 xor 1=11=1
3. If a=1a=1, b=1b=1, and c=0c=0:
• (a(a and b)=(1b)=(1 and 1)=11)=1
• (notb(notb and c)=(not1c)=(not1 and 0)=00)=0
• (a(a and b)b) xor (notb(notb and c)=1c)=1 xor 0=10=1
4. If a=1a=1, b=1b=1, and c=1c=1:
• (a(a and b)=(1b)=(1 and 1)=11)=1
• (notb(notb and c)=(not1c)=(not1 and 1)=01)=0
• (a(a and b)b) xor (notb(notb and c)=1c)=1 xor 0=10=1
So, the output of the VHDL code depends on the values of aa, bb, and cc, and it can be either 0 or 1 based on those values.

Is it just me or does there seem to be a LOT missing from the above ChatGPT answer.
It lists four conditions, but there are 3 input variables so there are 8 states...

So, the output of the VHDL code depends on the values of aa, bb, and cc, and it can be either 0 or 1 based on those values.
Genius!!! No Sh-- Sherlock.

I hope everybody in school these days just passes on the ChatGPT answers to questions like this.

As the two AND parts use B and /B, they can never both give a true simultaneously, so the XOR is redundant; it functions as an OR gate in this.

Both A and B true result in a true, via the first AND.
B false and C true result in a true, via the second AND.
All other states give false.

To the OP - just to be clear, the result in #1 is correct.

I don't know exactly what ChatGPT was asked, but the answer in #2 is wrong (or rather, not complete... it missed a=0, b=0, c=1 --> y=1, so #2 would give a result y = ac + ab).

### y<=(a and b) xor (not b and c);What's the output of this VHDL code where a, b, and c can be 0 or 1.​

Sure, let's evaluate the expression for all possible combinations of 0 and 1 for variables a, b, and c:

1. a=0, b=0, c=0:
y <= (0 and 0) xor (not 0 and 0)
y <= (0) xor (1 and 0)
y <= 0 xor 0
y <= 0

2. a=0, b=0, c=1:
y <= (0 and 0) xor (not 0 and 1)
y <= (0) xor (1 and 1)
y <= 0 xor 1
y <= 1

3. a=0, b=1, c=0:
y <= (0 and 1) xor (not 1 and 0)
y <= (0) xor (0 and 0)
y <= 0 xor 0
y <= 0

4. a=0, b=1, c=1:
y <= (0 and 1) xor (not 1 and 1)
y <= (0) xor (0 and 1)
y <= 0 xor 0
y <= 0

5. a=1, b=0, c=0:
y <= (1 and 0) xor (not 0 and 0)
y <= (0) xor (1 and 0)
y <= 0 xor 0
y <= 0

6. a=1, b=0, c=1:
y <= (1 and 0) xor (not 0 and 1)
y <= (0) xor (1 and 1)
y <= 0 xor 1
y <= 1

7. a=1, b=1, c=0:
y <= (1 and 1) xor (not 1 and 0)
y <= (1) xor (0 and 0)
y <= 1 xor 0
y <= 1

8. a=1, b=1, c=1:
y <= (1 and 1) xor (not 1 and 1)
y <= (1) xor (0 and 1)
y <= 1 xor 0
y <= 1

So, the outputs for all possible combinations of 0 and 1 for variables a, b, and c are:
- y = 0, 1, 0, 0, 0, 1, 1, 1

Last edited:
Well, that's a different answer than was given before, and it's correct this time.

Do you remember what you asked it at first to get the result in #2?

Well, that's a different answer than was given before, and it's correct this time.

Do you remember what you asked it at first to get the result in #2?
See bold in the post. The first time was exactly the title of this thread.

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