simple 16bit signal arithmetic problem

Hello

I have a question about N bit signal arithmetic.

I want to calculate (16bit input 1) - (16bit input 2), but 'adder' or 'sum' block shows weird results.

The blocks subtract like this way: (assuming that the signals are 8 bits for an example)

ex) (0 0 0 1 1 1 0 0) - (1 1 1 1 1 1 1 1) = (-1 -1 -1 0 0 0 -1 -1)

Is there any way to calculate binary codes?

Should I make digital adder?

Answer 1

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Addition and Subtraction blocks in simulink performs integer addition and subtraction, not bitwise.

What is your expectation for bitwise operation ?

Addition:

0 0 --> 0
0 1 --> 1
1 0 --> 1
1 1 --> ? What about carry ?

Subtraction:

0 0 --> 0
0 1 --> ? Borrow ?
1 0 --> 1
1 1 --> 0

Depending upon your expectation, you can extracts the bits from your integer and construct the logic using Logical blocks to perform the bitwise operation.