Binary to BCD

Binary to BCD Algorithm for converting N-bit binary number to BCD: 1. Set up a Result Shift Register (RSR) and a Binary Shift Register (BSR). 2. Clear the RSR and load Binary value into BSR. Set count to 1. 3. Shift most significant bit (MSB) of BSR into least significant bit (LSB) of RSR. 4. If cont = N then exit else: 5. Check each BCD digit of RSR. For BCD digits  5 add 3 to that digit. 6. Increment count. 7. Go to step 3.

Example: Consider 0FFH = 255. Let N = 12. Count RSR BSR Step 1 0000 0000 0000 0000 1111 1111 2 0000 0000 0000 0001 1111 111- 3 - Shift 0000 0000 0000 0001 1111 111- 5 – add 3 if  5 2 0000 0000 0000 0011 1111 11-- 3 - Shift 0000 0000 0000 0011 1111 11-- 5 – add 3 if  5 3 0000 0000 0000 0111 1111 1--- 3 - Shift 0000 0000 0000 0111 1111 1--- 5 – add 3 if  5 4 0000 0000 0000 1111 1111 ---- 3 - Shift 0000 0000 0000 1111 1111 ---- 5 – add 3 if  5 5 0000 0000 0001 1111 111- ---- 3 - Shift 0000 0000 0001 1111 111- ---- 5 – add 3 if  5 6 0000 0000 0011 1111 11------3 - Shift 0000 0000 0011 1111 11------5 – add 3 if  5 7 0000 0000 0111 1111 1------3 - Shift 0000 0000 0011 5 – add 3 if  5 0000 0000 1010 1111 1------8 0000 0001 0101 1111 ------3 - Shift 0000 0000 0011 5 – add 3 if  5 0000 0001 1000 9 0000 0011 0001 111------3 - Shift 0000 0011 0001 111------5 – add 3 if  5 10 0000 0110 0011 11------3 - Shift 0000 0011 0000 5 – add 3 if  5 0000 1001 0011 11------11 0001 0010 0111 1------3 - Shift 0000 0000 0011 5 – add 3 if  5 0001 0010 1010 1------12 0010 0101 0101 ------3 - Shift

1 Func_to_BCD Using the above algorithm write the function to_bcd that converts a 16 bit unsigned binary value to BCD.

-- pkg_func.vcd V 1.0 1/30/09 library IEEE; use IEEE.STD_LOGIC_1164.ALL; use IEEE.STD_LOGIC_ARITH.ALL; use IEEE.STD_LOGIC_UNSIGNED.ALL; package pkg_func is function to_bcd (binary: std_logic_vector) return std_logic_vector; end pkg_func; library IEEE; use IEEE.STD_LOGIC_1164.ALL; use IEEE.STD_LOGIC_ARITH.ALL; use IEEE.STD_LOGIC_UNSIGNED.ALL; package body pkg_func is ------Function: to_bcd - Converts 16 bit input to BCD. If input > 9999 then -- returns x"9999". -- Input: binary - 16 bit unsigned value. -- Returns: BCD unsigned. -- Ussage: BCD = to_bcd(binary); ------function to_bcd(binary: std_logic_vector) return STD_LOGIC_VECTOR is variable rsr : std_logic_vector(15 downto 0); -- Shift reg for BCD result variable bsr : std_logic_vector(15 downto 0); -- Shift reg for binary input variable correction : std_logic_vector(15 downto 0); -- Add to do BCD correction begin if CONV_INTEGER(binary) > 9999 then rsr := x"9999"; else -- Enter your code to complete this function.

end if; return rsr; end to_bcd; end pkg_func;

2 -- tb_to_bcd.vhd Version 1.0 by Dr. Jerry H. Tucker -- Test bench for function to_bcd in pkg_func.vhd -- Created 1/30/09 library IEEE; use IEEE.STD_LOGIC_1164.ALL; use IEEE.STD_LOGIC_ARITH.ALL; use IEEE.STD_LOGIC_UNSIGNED.ALL; use work.all; use pkg_func.all; -- uses to_bcd in package pkg_func.vhd entity tb is end tb; architecture test of tb is signal bi, bcd: std_logic_vector(15 downto 0) := x"ffff"; signal int: integer; begin -- Use linear feedback shift register to generate random binary values values. bi <= (bi(5) xor bi(3) xor bi(2) xor bi(0)) &bi(15 downto 1) after 5 ns; int <= conv_integer(bi); -- Get integer value of binary bcd <= to_bcd(bi); end test;

3 The waveform values are displayed in hexadecimal. You can select a signal and right click to change the radix or you can set all signal to hexadecimal by typing radix –hexadecimal in the transcript window.