Arithmetic operations in vhdl

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mohit1108

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I have made a program for PI controller and the excerpts are as follows-
v1<= v_prev + (k1*iq_error)+(k2*f_prev1)+(k3*f_prev2);
All the variables are std logic vector ( 7 downto 0)
but there is an error in execution of this code-

* can not have such operands in this context.

I have also included IEEE.NUMERIC_STD.ALL; but still error persists.

please help me out
 

try casting the std_logic_vectors to unsigned/signed, or better yet, just use unsigned/signed in the first place.

v1<= v_prev + (unsigned(k1)*unsigned(iq_error))+(unsigned(k2)*unsigned(f_prev1))+(unsigned(k3)*unsigned(f_prev2));

what would you do for a slv if you had a 'X' * 'H'?

https://www.synthworks.com/papers/vhdl_math_tricks_mapld_2003.pdf
 
Last edited:

gbounce said:
what would you do for a slv if you had a 'X' * 'H'?
Click to expand...

remember that signed/unsigned are arrays of std_logic too, so you could have 'x' * 'h'. you should just get 'x' as the result.
 

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