Question

Is it possible to write a code segment and call it, instead of writing that segment many times? Ie. I want to reuse a segment of code as shown below:

process (currentState)
begin
    case currentState is
    when requiredCoinsTensAnode => anodes <= "100000";--turn on the tens display
        case tensCount is
        when "0000" => segDisplay <= "1111110"; --0
        when "0001" => segDisplay <= "0110000"; --1
        when "0010" => segDisplay <= "1101101"; --2
        when "0011" => segDisplay <= "1111001"; --3
        when "0100" => segDisplay <= "0110011"; --4
        when "0101" => segDisplay <= "1011011"; --5
        when "0110" => segDisplay <= "1011111"; --6
        when "0111" => segDisplay <= "1110000"; --7
        when "1000" => segDisplay <= "1111111"; --8
        when others => segDisplay <= "1111011"; --9
        end case;
        nextState <= requiredCoinsUnitsAnode;--just displayed the tens digit, next we need to display the units digit
    when requiredCoinsUnitsAnode => anodes <= "010000";--turn on the units display
        case unitsCount is
        when "0000" => segDisplay <= "1111110"; --0
        when "0001" => segDisplay <= "0110000"; --1
        when "0010" => segDisplay <= "1101101"; --2
        when "0011" => segDisplay <= "1111001"; --3
        when "0100" => segDisplay <= "0110011"; --4
        when "0101" => segDisplay <= "1011011"; --5
        when "0110" => segDisplay <= "1011111"; --6
        when "0111" => segDisplay <= "1110000"; --7
        when "1000" => segDisplay <= "1111111"; --8
        when others => segDisplay <= "1111011"; --9
        end case;
        nextState <= insertedCoinsTensAnode;
    end case;
end process;

Answer 1

Functions are one option, as ravi has pointed out.

function f_segDisplay (
  signal segCount : std_logic_vector(6 downto 0))
  return std_logic_vector(3 downto 0) is
begin  -- f_segDisplay
    case segCount is
      when "0000" => return "1111110";  --0
      when "0001" => return "0110000";  --1
      when "0010" => return "1101101";  --2
      when "0011" => return "1111001";  --3
      when "0100" => return "0110011";  --4
      when "0101" => return "1011011";  --5
      when "0110" => return "1011111";  --6
      when "0111" => return "1110000";  --7
      when "1000" => return "1111111";  --8
      when others => return "1111011";  --9
    end case;
end f_segDisplay;

process (currentState, tensCount, unitsCount)
begin
  case currentState is
    when requiredCoinsTensAnode =>
      anodes     <= "100000";          --turn on the tens display
      segDisplay <= f_segDisplay(tensCount);
      nextState  <= requiredCoinsUnitsAnode;
    when requiredCoinsUnitsAnode =>
      anodes     <= "010000";          --turn on the units display
      segDisplay <= f_segDisplay(unitsCount);
      nextState  <= insertedCoinsTensAnode;
  end case;
end process;

Depending on the compiler and options, it may decide to put the function code in-line. This would cause multiple instances of the logic to be placed, much like your original code.

An alternative is that you take the common code out into another process:

p_segdisplay : process (segCount)
begin  -- process p_segdisplay
  case segCount is
    when "0000" => segDisplay <= "1111110";  --0
    when "0001" => segDisplay <= "0110000";  --1
    when "0010" => segDisplay <= "1101101";  --2
    when "0011" => segDisplay <= "1111001";  --3
    when "0100" => segDisplay <= "0110011";  --4
    when "0101" => segDisplay <= "1011011";  --5
    when "0110" => segDisplay <= "1011111";  --6
    when "0111" => segDisplay <= "1110000";  --7
    when "1000" => segDisplay <= "1111111";  --8
    when others => segDisplay <= "1111011";  --9
  end case;
end process p_segdisplay;

process (currentState, tensCount, unitsCount)
begin
  case currentState is
    when requiredCoinsTensAnode =>
      anodes    <= "100000";          --turn on the tens display
      segCount  <= tensCount;
      nextState <= requiredCoinsUnitsAnode;
    when requiredCoinsUnitsAnode =>
      anodes    <= "010000";          --turn on the units display
      segCount  <= unitsCount;
      nextState <= insertedCoinsTensAnode;
  end case;
end process;

BTW: You need tensCount and unitsCount in your sensitivity list.

Abstracting a common resource like this is a useful technique when doing area or power concious designs.

Both should work in the same way, and perfect tools would produce the same logic from the two, but we rarely have perfect tools. Experiment with different styles. Some produce better results on some tools, some on others.