# \[Marlin] M109 - Wait for Hotend Temperature

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**📅Update: 2020/09/18**
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## Description

This command optionally sets a new target hot end temperature and waits for the target temperature to be reached before proceeding. If the temperature is set with `S` then [`M109`](https://app.gitbook.com/docs/gcode/M109.html) waits *only when heating*. If the temperature is set with `R` then [`M109`](https://app.gitbook.com/docs/gcode/M109.html) will also wait for the temperature to go down.

## Notes

* With `PRINTJOB_TIMER_AUTOSTART` this command will start the print job if heating, and stop the print job timer if the temperature is set at or below half of `EXTRUDE_MINTEMP`.
* This command (as well as [`M109`](https://app.gitbook.com/docs/gcode/M109.html) and [`M190`](https://app.gitbook.com/docs/gcode/M190.html)) can block new commands from the host, preventing remote shutdown. However, if `EMERGENCY_PARSER` is enabled, a host can send [`M108`](https://app.gitbook.com/docs/gcode/M108.html) to break out of the wait loop.
* To set the hot end temperature and proceed without waiting, use [`M104`](https://app.gitbook.com/docs/gcode/M104.html).

## Usage

`M109` `[B<temp>]` `[F<flag>]` `[I<index>]` `[R<temp>]` `[S<temp>]` `[T<index>]`

### Parameters

* `[B<temp>]` With `AUTOTEMP`, the max auto-temperature.
* `[F<flag>]` Autotemp flag. Omit to disable autotemp.
* `[I<index>]` Material preset index. Overrides `S`.
* `[R<temp>]` Target temperature (wait for cooling or heating).
* `[S<temp>]` Target temperature (wait only when heating). Also `AUTOTEMP`: The min auto-temperature.
* `[T<index>]` Hotend index. If omitted, the currently active hotend will be used.

## Examples

Set target temperature and wait (if heating up)

```
M109 S180
```

Set target temperature, wait even if cooling

```
M109 R120
```

Set target temperature for E1 and wait (if heating up)

```
M109 T1 R205
```

`AUTOTEMP`: Set autotemp range, wait for temp

```
M109 F S180 B190
```

'`AUTOTEMP`: Disable autotemp, wait for temp'

```
M109
```


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