按第一个按键则数码管数字加一，按第二个按键则数码管数字减一，按第三个则数字左移，在最右边输入

add_outside: process(clk,reset_all)   --key1:按键加一，后半部分为当清屏信号到来时，外部输入密码置0
      begin
        if(key1'event and key1='0') then
           key1_clear <= '1';
            case location is
              when "00" => bit_one_out <= bit_one_out + 1;
                if(bit_one_out = 9) then
                   bit_one_out <= 0;
                  end if;
                when "01" => bit_two_out <= bit_two_out + 1;
                 if(bit_two_out = 9) then
                    bit_two_out <= 0;
                  end if;
                when "10" => bit_three_out <= bit_three_out + 1;
                 if(bit_three_out = 9) then
                    bit_three_out <= 0;
                  end if;
                when "11" => bit_four_out <= bit_four_out + 1;
                 if(bit_four_out = 9) then
                    bit_four_out <= 0;
                  end if;
            end case;
          end if;
          if(clear_num=0) then
            key1_clear <= '0';
          end if;
          if(reset_all='1') then
            bit_one_out <= 0;
             bit_two_out <= 0;
             bit_three_out <= 0;
             bit_four_out <= 0;
          end if;
  end process add_outside;
  
  sub_outside: process(clk,reset_all)  --key2
   begin
        if(key2'event and key2='0') then
           key2_clear <= '1';
            
            case location is
              when "00" => bit_one_out <= bit_one_out - 1;
                if(bit_one_out = 0) then
                   bit_one_out <= 9;
                  end if;
                when "01" => bit_two_out <= bit_two_out - 1;
                 if(bit_two_out = 0) then
                    bit_two_out <= 9;
                  end if;
                when "10" => bit_three_out <= bit_three_out - 1;
                 if(bit_three_out = 0) then
                    bit_three_out <= 9;
                  end if;
                when "11" => bit_four_out <= bit_four_out - 1;
                 if(bit_four_out = 0) then
                    bit_four_out <= 9;
                  end if;
            end case;
         
          end if;
          if(clear_num=0) then
            key2_clear <= '0';
          end if;
         
    end process sub_outside;
此程序出错，不可以在两个进程对同一个赋值