Converting 8 bit binary to BCD using integers

Question

OK hello all , what i am trying to do in VHDL is take an 8 bit binary value and represent it as BCD but theres a catch as this calue must be a fraction of the maximum input which is 9.

1- Convert input to Integer e.g 1000 0000 -> 128

2- Divide integer by 255 then multiply by 90 ( 90 so that i get the one's digit and the first digit after the decimal point to be all after the decimal point)

E.g 128/255*90 = 45.17 ( let this be signal_in)

3.Extract the two digits of 45 by dividing by 20 and store them as separate integers e.g I would use something like:

LSB_int = signal_in mod 10

Then i would divide signal in by 10 hence changing it to 4.517 then let that equal to MSB_int.. (that would truncate the decimals and store 4 right)

4.Convert both the LSB_int and MSB_int to 4 digit BCD

..and i would be perfect from there...But sadly i got so much trouble...with different data types (signed unsigend std_logic_vectors)and division.So i just need help with any flaws in my thought process and things i should look out for when doing this..

I actually did over my code and thought i saved this one..but i didn't and well i still believe this solution can work i would reply with what i think was my old code...as soon as i could remember it all..

Here is my other question with my new code..(just to show i did do something..) Convert 8bit binary number to BCD in VHDL

Note an 8 bit value only requires 3 BCD digits to express (the maximum value is 255). Do you have a specific question? Perhaps you could show your code and ask about specific syntactical or semantic errors? Incorrect results? — , Nov 23 '14 at 08:16

score 0 · Accepted Answer · answered Nov 26 '14 at 19:01

f I understand well, what you need is to convert an 8bit data

0-255 → 0-9000

and represent it with 4 BCD digit.

For example You want 0x80 → 4517 (BCD)

If so I suggest you a totally different idea:

1)

let convert input range in output range with a simple 8bit*8bit->16bit

(in_data * 141) and keep the 14 MSB (0.1% error)

And let say this 14 bit register is the TARGET

2)

Build a 4 digit BCD Up/Down counter (your output)

Build a 14bit Binary Up/Down counter (follower)

Supply both with the same input (reset, clk, UpDown)

(making one the shadow of the other)

3)

Compare TARGET and the binary counter

if (follower < target) then increment the counters
else if (follower > target) then decrements the counters
else nothing

4)

end

Converting 8 bit binary to BCD using integers

1 Answers1