---
name: "pcf8591"
section: "4"
platform: "freebsd"
package: "base"
version: "16.0-CURRENT-20261027-61c70dc16a79"
release: "FreeBSD 16.0-CURRENT (2026-10-27)"
platforms: ["freebsd"]
url: "https://new.carta.tech/pcf8591"
---

# pcf8591(4)

driver for the PCF8591 8-bit A/D and D/A converter

## NAME

**pcf8591** – driver for the PCF8591 8-bit A/D and D/A converter

## SYNOPSIS

To compile this driver into the kernel, place the following lines in your kernel configuration file:

**device pcf8591** **device iicbus**

Alternatively, to load the driver as a module at boot time, place the following line in [loader.conf(5)](/loader.conf/5.md):

```
pcf8591_load="YES"
```

## DESCRIPTION

The **pcf8591** driver supports reading four inputs and setting one output over I2C. The hardware supports configuring the input lines as:

- four single-ended inputs

- three differential inputs (one input line is shared between all three inputs)

- two single-ended inputs and one differential input

- two differential inputs.

The **pcf8591** driver reports data via [sysctl(8)](/sysctl/8.md) entries in the device's node in the [sysctl(8)](/sysctl/8.md) tree:

- *inputs.%d*

  The input level of the corresponding input in steps between 0 and 255. Absolute voltage depends on an actual reference voltage.

On an [FDT(4)](/FDT/4.md) based system the following properties must be set:

- *compatible*

  Must be set to "nxp,pcf8591".

- *reg*

  The I2C address of **pcf8591**. It should be in the range from 0x40 to 0x4f (7-bit).

The DTS part for a **pcf8591** device usually looks like:

```
/ {
	...
	pcf8591adc {
		compatible = "nxp,pcf8591";
		reg = <0x48>;
	};
};
```

## SEE ALSO

[fdt(4)](/fdt/4.md), [iicbus(4)](/iicbus/4.md), [sysctl(8)](/sysctl/8.md)

## HISTORY

The **pcf8591** driver and this manual page was written by Andriy Gapon ⟨*avg@FreeBSD.org*⟩.

## BUGS

The **pcf8591** driver does not support changing the input configuration. All input lines are configured as single-ended inputs.

The **pcf8591** driver does not support setting the output. It is always disabled (tri-state).