---
name: "lm"
section: "4"
platform: "openbsd"
package: "man"
version: "8.0-current-20261101"
release: "OpenBSD 8.0-current (2026-11-01)"
platforms: ["openbsd"]
url: "https://new.carta.tech/lm/4"
---

# lm(4)

National Semiconductor LM78/79/81 temperature, voltage, and fan sensor

## NAME

**lm** – National Semiconductor LM78/79/81 temperature, voltage, and fan sensor

## SYNOPSIS

**lm0 at isa? port 0x290** **lm1 at isa? port 0x280** **lm2 at isa? port 0x310** **lm\* at iic?** **lm\* at wbsio?**

## DESCRIPTION

The **lm** driver provides support for the National Semiconductor LM78/79/81 hardware monitors and register compatible chips to be used with the [sysctl(8)](/sysctl/8.md) interface.

The original LM78 hardware monitor supports 11 sensors:

| | | |
| --- | --- | --- |
| **Sensor** | **Units** | **Typical Use** |
| IN0 | uV DC | Core voltage |
| IN1 | uV DC | Unknown |
| IN2 | uV DC | +3.3V |
| IN3 | uV DC | +5V |
| IN4 | uV DC | +12V |
| IN5 | uV DC | -12V |
| IN6 | uV DC | -5V |
| Temp | uK | Motherboard Temperature |
| Fan0 | RPM | Fan |
| Fan1 | RPM | Chassis Fan |
| Fan2 | RPM | Fan |

For other devices, sensors' names and numbers will be different.

## HARDWARE

Chips supported by the **lm** driver include:

- ASUS AS99127F

- National Semiconductor LM78 and LM78-J

- National Semiconductor LM79

- National Semiconductor LM81

- Nuvoton NCT6775F, NCT6776F, NCT6779D, NCT6791D, NCT6792D, NCT6793D, NCT6795D

- Winbond W83627HF, W83627THF, W83637HF and W83697HF

- Winbond W83627DHG, W83627UHG and W83627EHF

- Winbond W83781D, W83782D and W83783S

- Winbond W83791D, W83791SD and W83792D

Some devices can attach to both [iic(4)](/iic/4.md) and [isa(4)](/isa/4.md); others can only attach to either one or the other. If the **lm** driver detects a device attaching to both [iic(4)](/iic/4.md) and [isa(4)](/isa/4.md), it will detach the device from [iic(4)](/iic/4.md).

## SEE ALSO

[iic(4)](/iic/4.md), [isa(4)](/isa/4.md), [wbsio(4)](/wbsio/4.md), [sensorsd(8)](/sensorsd/8.md), [sysctl(8)](/sysctl/8.md)

## HISTORY

The **lm** driver first appeared in NetBSD 1.5; OpenBSD support was added in OpenBSD 3.4.

## AUTHORS

The **lm** driver was written by Bill Squier and ported to OpenBSD 3.4 by Alexander Yurchenko ⟨*grange@openbsd.org*⟩. The driver was largely rewritten for OpenBSD 3.9 by Mark Kettenis ⟨*kettenis@openbsd.org*⟩.

## CAVEATS

Some vendors connect these chips to non-standard thermal diodes and resistors. This will result in bogus sensor values.

## BUGS

Interrupt support is unimplemented.

There are currently no known pnpbios IDs assigned to LM chips.

This driver attaches to the Winbond W83791SD chip even though that chip does not have any sensors.