一位通信协议

一些非常简单和低成本的硬件设备，如传感器，使用一位通信协议。单条双向数据线将设备连接到一种微控制器。它通常由上拉电阻上拉。通信设备将线路驱动为低预定义持续时间以将信息发送到另一个。下图说明了这一点：

此示例显示如何使用 ieee.std_logic_1164.std_logic 已解析类型对此进行建模。

-- File md.vhd
library ieee;
use ieee.std_logic_1164.all;

entity one_bit_protocol is
end entity one_bit_protocol;

architecture arc of one_bit_protocol is

  component uc is
    port(
      data_in: in  std_ulogic;
      set_low: out std_ulogic
    );
  end component uc;

  component sensor is
    port(
      data_in: in  std_ulogic;
      set_low: out std_ulogic
    );
  end component sensor;

  signal data:           std_logic;  -- The bi-directional data line
  signal set_low_uc:     std_ulogic;
  signal set_low_sensor: std_ulogic;

begin

  -- Micro-controller
  uc0: uc port map(
    data_in => data,
    set_low => set_low_uc
  );

  -- Sensor
  sensor0: sensor port map(
    data_in => data,
    set_low => set_low_sensor
  );

  data <= 'H'; -- Pull-up resistor

  -- Micro-controller 3-states buffer
  data <= '0' when set_low_uc = '1' else 'Z';

  -- Sensor 3-states buffer
  data <= '0' when set_low_sensor = '1' else 'Z';

end architecture arc;