handling bit_vectors/integers

[blues82]

I am working on a project in which I am taking to inputs..say 2 and 4. From these I need to create 24. Like using a tv remote control. Any suggestions at all would be appreciated. This is the final piece of my puzzle and an urgent fix is needed.

 

[VHDLguy]

well it depends... if you are talking hex then its easy.
but I am guessing you want decimal... not so easy.

I will assume that the inputs can only be 0-9. You result could therefore by 0 - 99 which means we need 7 bits.

So, now you need res = num1*10 + num2

multiplying by 10 may not be an option, so instead lets change it to

res = num1*8 + num1*2 + num2.

so declare a signal called num1x8 and num1x2.
num1 and num2 will be 4 bits each. so num1x8 will be 7 bits and num1x2 will be 5 bits
num1x2 <= num1 & '0';
num1x8 <= num1 & "000";

so now res <= num1x8 + num1x2 + num2;

we know that the result will be less than 99, but the synthesizer won't know that. It will probably complain if you make res a 7 bit number.

so you can either make res 8 bits and only use the lowest 7 bits, or you can say
res <= (num1x8 + num1x2 + num2)(6 downto 0);

I think that should work.

Anyway, you should be able to get their from what I have told you.

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