---
name: "lut5"
section: "9"
platform: "linux"
package: "linuxcnc-uspace"
version: "1:2.9.4-2+deb13u1"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/lut5"
---

# lut5(9)

Arbitrary 5-input logic function based on a look-up table

## NAME

lut5 - Arbitrary 5-input logic function based on a look-up table

## SYNOPSIS

**loadrt lut5 \[count=*N*\|names=*name1*\[,*name2...*\]\]**

## DESCRIPTION

**lut5** constructs a logic function with up to 5 inputs using a **l**ook-**u**p **t**able. The value for **function** can be determined by writing the truth table, and computing the sum of **all** the **weights** for which the output value would be TRUE. The weights are hexadecimal not decimal so hexadecimal math must be used to sum the weights. A wiki page has a calculator to assist in computing the proper value for function.

https://wiki.linuxcnc.org/cgi-bin/wiki.pl?Lut5

Note that LUT5 will generate any of the 4,294,967,296 logical functions of 5 inputs so **AND**, **OR**, **NAND**, **NOR**, **XOR** and every other combinatorial function is possible.

### Example Functions

A 5-input *and* function is TRUE only when all the inputs are true, so the correct value for **function** is **0x80000000**.

A 2-input *or* function would be the sum of **0x2** + **0x4** + **0x8**, so the correct value for **function** is **0xe**.

A 5-input *or* function is TRUE whenever any of the inputs are true, so the correct value for **function** is **0xfffffffe**. Because every weight except **0x1** is true the function is the sum of every line except the first one.

A 2-input *xor* function is TRUE whenever exactly one of the inputs is true, so the correct value for **function** is **0x6**.  Only **in-0** and **in-1** should be connected to signals, because if any other bit is **TRUE** then the output will be **FALSE**.

| | | | | | |
| --- | --- | --- | --- | --- | --- |
| **Weights for each line of truth table** |
| **Bit 4** | **Bit 3** | **Bit 2** | **Bit 1** | **Bit 0** | **Weight** |
| 0 | 0 | 0 | 0 | 0 | 0x1 |
| 0 | 0 | 0 | 0 | 1 | 0x2 |
| 0 | 0 | 0 | 1 | 0 | 0x4 |
| 0 | 0 | 0 | 1 | 1 | 0x8 |
| 0 | 0 | 1 | 0 | 0 | 0x10 |
| 0 | 0 | 1 | 0 | 1 | 0x20 |
| 0 | 0 | 1 | 1 | 0 | 0x40 |
| 0 | 0 | 1 | 1 | 1 | 0x80 |
| 0 | 1 | 0 | 0 | 0 | 0x100 |
| 0 | 1 | 0 | 0 | 1 | 0x200 |
| 0 | 1 | 0 | 1 | 0 | 0x400 |
| 0 | 1 | 0 | 1 | 1 | 0x800 |
| 0 | 1 | 1 | 0 | 0 | 0x1000 |
| 0 | 1 | 1 | 0 | 1 | 0x2000 |
| 0 | 1 | 1 | 1 | 0 | 0x4000 |
| 0 | 1 | 1 | 1 | 1 | 0x8000 |
| 1 | 0 | 0 | 0 | 0 | 0x10000 |
| 1 | 0 | 0 | 0 | 1 | 0x20000 |
| 1 | 0 | 0 | 1 | 0 | 0x40000 |
| 1 | 0 | 0 | 1 | 1 | 0x80000 |
| 1 | 0 | 1 | 0 | 0 | 0x100000 |
| 1 | 0 | 1 | 0 | 1 | 0x200000 |
| 1 | 0 | 1 | 1 | 0 | 0x400000 |
| 1 | 0 | 1 | 1 | 1 | 0x800000 |
| 1 | 1 | 0 | 0 | 0 | 0x1000000 |
| 1 | 1 | 0 | 0 | 1 | 0x2000000 |
| 1 | 1 | 0 | 1 | 0 | 0x4000000 |
| 1 | 1 | 0 | 1 | 1 | 0x8000000 |
| 1 | 1 | 1 | 0 | 0 | 0x10000000 |
| 1 | 1 | 1 | 0 | 1 | 0x20000000 |
| 1 | 1 | 1 | 1 | 0 | 0x40000000 |
| 1 | 1 | 1 | 1 | 1 | 0x80000000 |

## FUNCTIONS

- **lut5.***N*

  ## PINS

- **lut5.*N*.in-0 bit in**

  - **lut5.*N*.in-1 bit in**

  - **lut5.*N*.in-2 bit in**

  - **lut5.*N*.in-3 bit in**

  - **lut5.*N*.in-4 bit in**

  - **lut5.*N*.out bit out**

  ## PARAMETERS

- **lut5.*N*.function u32 rw**

  ## SEE ALSO

**and**(9), [**logic**(9)](/logic/9.md), [**not**(9)](/not/9.md), [**or2**(9)](/or2/9.md), [**xor2**(9)](/xor2/9.md).

## AUTHOR

Jeff Epler

## LICENSE

GPL