> For the complete documentation index, see [llms.txt](https://book.bsdcn.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://book.bsdcn.org/man/man4/pcf8574.4.md).

# pcf8574.4

`pcf8574` — PCF8574 8 位 I2C IO 扩展器驱动

## 名称

`pcf8574`

## 概要

`要将此驱动编译进内核，请在你的内核配置文件中加入以下行：`

> device pcf8574 device gpio device iicbus

`或者，要在引导时以模块形式加载此驱动，请在 loader.conf(5) 中加入以下行：`

```sh
pcf8574_load="YES"
```

## 描述

`pcf8574` 驱动通过 gpiobus(4) 对 8 个 GPIO 引脚进行控制。这些引脚为准双向引脚。仅低电平输出可被主动驱动；高电平输出等价于输入。

在基于 [fdt(4)](/man/man4/fdt.4.md) 的系统上，必须设置以下属性：

**`compatible`** 必须设为“nxp,pcf8574”。

**`reg`** `pcf8574` 的 I2C 地址。

`pcf8574` 设备的 DTS 部分通常如下所示：

```sh
/ {
	...
	pcf8574@27 {
		compatible = "nxp,pcf8574";
		reg = <0x27>;
	};
};
```

## 参见

[fdt(4)](/man/man4/fdt.4.md), gpiobus(4), [iicbus(4)](/man/man4/iicbus.4.md)

## 历史

`pcf8574` 驱动及本手册页由 Andriy Gapon <avg@FreeBSD.org> 编写。

## 缺陷

`pcf8574` 驱动不支持硬件提供的输入变化中断。


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