---
title: Keyboard Scan Configuration
sidebar_label: Keyboard Scan
---

See [Configuration Overview](index.md) for instructions on how to change these settings.

## Common

### Kconfig

Definition files:

- [zmk/app/Kconfig](https://github.com/zmkfirmware/zmk/blob/main/app/Kconfig)
- [zmk/app/module/drivers/kscan/Kconfig](https://github.com/zmkfirmware/zmk/blob/main/app/module/drivers/kscan/Kconfig)

| Config                                 | Type | Description                                          | Default |
| -------------------------------------- | ---- | ---------------------------------------------------- | ------- |
| `CONFIG_ZMK_KSCAN_EVENT_QUEUE_SIZE`    | int  | Size of the event queue for kscan events             | 4       |
| `CONFIG_ZMK_KSCAN_INIT_PRIORITY`       | int  | Keyboard scan device driver initialization priority  | 40      |
| `CONFIG_ZMK_KSCAN_DEBOUNCE_PRESS_MS`   | int  | Global debounce time for key press in milliseconds   | -1      |
| `CONFIG_ZMK_KSCAN_DEBOUNCE_RELEASE_MS` | int  | Global debounce time for key release in milliseconds | -1      |

If the debounce press/release values are set to any value other than `-1`, they override the `debounce-press-ms` and `debounce-release-ms` devicetree properties for all keyboard scan drivers which support them. See the [debouncing documentation](../features/debouncing.md) for more details.

### Devicetree

Applies to: [`/chosen` node](https://docs.zephyrproject.org/3.5.0/build/dts/intro-syntax-structure.html#aliases-and-chosen-nodes)

| Property               | Type | Description                                                            |
| ---------------------- | ---- | ---------------------------------------------------------------------- |
| `zmk,kscan`            | path | The node for the keyboard scan driver to use                           |
| `zmk,matrix-transform` | path | The node for the [matrix transform](layout.md#matrix-transform) to use |

## Demux Driver

Keyboard scan driver which works like a regular matrix but uses a demultiplexer to drive the rows or columns. This allows N GPIOs to drive N<sup>2</sup> rows or columns instead of just N like with a regular matrix.

:::note
Currently this driver does not honor the `CONFIG_ZMK_KSCAN_DEBOUNCE_*` settings.
:::

### Devicetree

Applies to: `compatible = "zmk,kscan-gpio-demux"`

Definition file: [zmk/app/module/dts/bindings/kscan/zmk,kscan-gpio-demux.yaml](https://github.com/zmkfirmware/zmk/blob/main/app/module/dts/bindings/kscan/zmk%2Ckscan-gpio-demux.yaml)

| Property                | Type       | Description                      | Default |
| ----------------------- | ---------- | -------------------------------- | ------- |
| `input-gpios`           | GPIO array | Input GPIOs                      |         |
| `output-gpios`          | GPIO array | Demultiplexer address GPIOs      |         |
| `debounce-period`       | int        | Debounce period in milliseconds  | 5       |
| `polling-interval-msec` | int        | Polling interval in milliseconds | 25      |

## Direct GPIO Driver

Keyboard scan driver where each key has a dedicated GPIO.

### Kconfig

Definition file: [zmk/app/module/drivers/kscan/Kconfig](https://github.com/zmkfirmware/zmk/blob/main/app/module/drivers/kscan/Kconfig)

| Config                            | Type | Description                                      | Default |
| --------------------------------- | ---- | ------------------------------------------------ | ------- |
| `CONFIG_ZMK_KSCAN_DIRECT_POLLING` | bool | Poll for key presses instead of using interrupts | n       |

### Devicetree

Applies to: `compatible = "zmk,kscan-gpio-direct"`

Definition file: [zmk/app/module/dts/bindings/kscan/zmk,kscan-gpio-direct.yaml](https://github.com/zmkfirmware/zmk/blob/main/app/module/dts/bindings/kscan/zmk%2Ckscan-gpio-direct.yaml)

| Property                  | Type       | Description                                                                                                | Default |
| ------------------------- | ---------- | ---------------------------------------------------------------------------------------------------------- | ------- |
| `input-gpios`             | GPIO array | Input GPIOs (one per key). Can be either direct GPIO pin or `gpio-key` references                          |         |
| `debounce-press-ms`       | int        | Debounce time for key press in milliseconds. Use 0 for eager debouncing                                    | 5       |
| `debounce-release-ms`     | int        | Debounce time for key release in milliseconds                                                              | 5       |
| `debounce-scan-period-ms` | int        | Time between reads in milliseconds when any key is pressed                                                 | 1       |
| `poll-period-ms`          | int        | Time between reads in milliseconds when no key is pressed and `CONFIG_ZMK_KSCAN_DIRECT_POLLING` is enabled | 10      |
| `toggle-mode`             | bool       | Use toggle switch mode                                                                                     | n       |
| `wakeup-source`           | bool       | Mark this kscan instance as able to wake the keyboard                                                      | n       |

Assuming the switches connect each GPIO pin to the ground, the [GPIO flags](https://docs.zephyrproject.org/3.5.0/hardware/peripherals/gpio.html#api-reference) for the elements in `input-gpios` should be `(GPIO_ACTIVE_LOW | GPIO_PULL_UP)`:

```dts
    kscan0: kscan {
        compatible = "zmk,kscan-gpio-direct";
        wakeup-source;
        input-gpios
            = <&pro_micro 4 (GPIO_ACTIVE_LOW | GPIO_PULL_UP)>
            , <&pro_micro 5 (GPIO_ACTIVE_LOW | GPIO_PULL_UP)>
            ;
    };
```

A direct pin defined in the `input-gpios` property is considered a column when used in a [matrix transform](layout.md#matrix-transform); e.g. the 5th pin on the list can be referred to using `RC(0,4)`.

By default, a switch will drain current through the internal pull up/down resistor whenever it is pressed. This is not ideal for a toggle switch, where the switch may be left in the "pressed" state for a long time. Enabling `toggle-mode` will make the driver enable and disable the internal pull up/down resistor as needed when the switch is toggled to minimise power draw. For `toggle-mode` to work correctly each pole of the switch needs a dedicated GPIO pin.

`toggle-mode` applies to all switches handled by the instance of the driver. To use a toggle switch with other, non-toggle, direct GPIO switches, create two instances of the direct GPIO driver, one with `toggle-mode` and the other without. Then, use a [composite driver](#composite-driver) to combine them. The state of the switch is read on power on, so if the switch is moved whilst the board is off this will get correctly interpreted by the driver.

When using `toggle-mode` the pull resistors get automatically set by the driver and should not be set in the devicetree via GPIO flags. Assuming the common pole of the switch is connected to ground with an SP3T switch:

```dts
    kscan_sp3t_toggle: kscan_sp3t_toggle {
        compatible = "zmk,kscan-gpio-direct";
        toggle-mode;

        input-gpios
        = <&pro_micro 4 GPIO_ACTIVE_LOW>
        , <&pro_micro 3 GPIO_ACTIVE_LOW>
        , <&pro_micro 2 GPIO_ACTIVE_LOW>
        ;
    };
```

## Matrix Driver

Keyboard scan driver where keys are arranged on a matrix with one GPIO per row and column.

Definition file: [zmk/app/module/drivers/kscan/Kconfig](https://github.com/zmkfirmware/zmk/blob/main/app/module/drivers/kscan/Kconfig)

| Config                                         | Type        | Description                                                               | Default |
| ---------------------------------------------- | ----------- | ------------------------------------------------------------------------- | ------- |
| `CONFIG_ZMK_KSCAN_MATRIX_POLLING`              | bool        | Poll for key presses instead of using interrupts                          | n       |
| `CONFIG_ZMK_KSCAN_MATRIX_WAIT_BEFORE_INPUTS`   | int (ticks) | How long to wait before reading input pins after setting output active    | 0       |
| `CONFIG_ZMK_KSCAN_MATRIX_WAIT_BETWEEN_OUTPUTS` | int (ticks) | How long to wait between each output to allow previous output to "settle" | 0       |

### Devicetree

Applies to: `compatible = "zmk,kscan-gpio-matrix"`

Definition file: [zmk/app/module/dts/bindings/kscan/zmk,kscan-gpio-matrix.yaml](https://github.com/zmkfirmware/zmk/blob/main/app/module/dts/bindings/kscan/zmk%2Ckscan-gpio-matrix.yaml)

| Property                  | Type       | Description                                                                                                | Default     |
| ------------------------- | ---------- | ---------------------------------------------------------------------------------------------------------- | ----------- |
| `row-gpios`               | GPIO array | Matrix row GPIOs in order, starting from the top row                                                       |             |
| `col-gpios`               | GPIO array | Matrix column GPIOs in order, starting from the leftmost row                                               |             |
| `debounce-press-ms`       | int        | Debounce time for key press in milliseconds. Use 0 for eager debouncing                                    | 5           |
| `debounce-release-ms`     | int        | Debounce time for key release in milliseconds                                                              | 5           |
| `debounce-scan-period-ms` | int        | Time between reads in milliseconds when any key is pressed                                                 | 1           |
| `diode-direction`         | string     | The direction of the matrix diodes                                                                         | `"row2col"` |
| `poll-period-ms`          | int        | Time between reads in milliseconds when no key is pressed and `CONFIG_ZMK_KSCAN_MATRIX_POLLING` is enabled | 10          |
| `wakeup-source`           | bool       | Mark this kscan instance as able to wake the keyboard                                                      | n           |

The `diode-direction` property must be one of:

| Value       | Description                                                           |
| ----------- | --------------------------------------------------------------------- |
| `"row2col"` | Diodes point from rows to columns (cathodes are connected to columns) |
| `"col2row"` | Diodes point from columns to rows (cathodes are connected to rows)    |

Given the `diode-direction`, the [GPIO flags](https://docs.zephyrproject.org/3.5.0/hardware/peripherals/gpio.html#api-reference) for the elements in `row-` and `col-gpios` should be set appropriately.
The output pins (e.g. columns for `col2row`) should have the flag `GPIO_ACTIVE_HIGH`, and input pins (e.g. rows for `col2row`) should have the flags `(GPIO_ACTIVE_HIGH | GPIO_PULL_DOWN)`:

```dts
    kscan0: kscan {
        compatible = "zmk,kscan-gpio-matrix";
        wakeup-source;
        diode-direction = "col2row";
        col-gpios
            = <&pro_micro 4 GPIO_ACTIVE_HIGH>
            , <&pro_micro 5 GPIO_ACTIVE_HIGH>
            ;
        row-gpios
            = <&pro_micro 6 (GPIO_ACTIVE_HIGH | GPIO_PULL_DOWN)>
            , <&pro_micro 7 (GPIO_ACTIVE_HIGH | GPIO_PULL_DOWN)>
            ;
    };
```

## Charlieplex Driver

Keyboard scan driver where keys are arranged on a matrix with each GPIO used as both input and output.

- With `interrupt-gpios` unset, this allows n pins to drive n\*(n-1) keys.
- With `interrupt-gpios` set, n pins will drive (n-1)\*(n-2) keys, but provide much improved power handling.

Definition file: [zmk/app/module/drivers/kscan/Kconfig](https://github.com/zmkfirmware/zmk/blob/main/app/module/drivers/kscan/Kconfig)

| Config                                              | Type        | Description                                                               | Default |
| --------------------------------------------------- | ----------- | ------------------------------------------------------------------------- | ------- |
| `CONFIG_ZMK_KSCAN_CHARLIEPLEX_WAIT_BEFORE_INPUTS`   | int (ticks) | How long to wait before reading input pins after setting output active    | 0       |
| `CONFIG_ZMK_KSCAN_CHARLIEPLEX_WAIT_BETWEEN_OUTPUTS` | int (ticks) | How long to wait between each output to allow previous output to "settle" | 0       |

### Devicetree

Applies to: `compatible = "zmk,kscan-gpio-charlieplex"`

Definition file: [zmk/app/module/dts/bindings/kscan/zmk,kscan-gpio-charlieplex.yaml](https://github.com/zmkfirmware/zmk/blob/main/app/module/dts/bindings/kscan/zmk%2Ckscan-gpio-charlieplex.yaml)

| Property                  | Type       | Description                                                                                 | Default |
| ------------------------- | ---------- | ------------------------------------------------------------------------------------------- | ------- |
| `gpios`                   | GPIO array | GPIOs used, listed in order.                                                                |         |
| `interrupt-gpios`         | GPIO array | A single GPIO to use for interrupt. Leaving this empty will enable continuous polling.      |         |
| `debounce-press-ms`       | int        | Debounce time for key press in milliseconds. Use 0 for eager debouncing.                    | 5       |
| `debounce-release-ms`     | int        | Debounce time for key release in milliseconds.                                              | 5       |
| `debounce-scan-period-ms` | int        | Time between reads in milliseconds when any key is pressed.                                 | 1       |
| `poll-period-ms`          | int        | Time between reads in milliseconds when no key is pressed and `interrupt-gpois` is not set. | 10      |
| `wakeup-source`           | bool       | Mark this kscan instance as able to wake the keyboard                                       | n       |

Define the transform with a [matrix transform](layout.md#matrix-transform). The row is always the driven pin, and the column always the receiving pin (input to the controller).
For example, in `RC(5,0)` power flows from the 6th pin in `gpios` to the 1st pin in `gpios`.
Exclude all positions where the row and column are the same as these pairs will never be triggered, since no pin can be both input and output at the same time.

The [GPIO flags](https://docs.zephyrproject.org/3.5.0/hardware/peripherals/gpio.html#api-reference) for the elements in `gpios` should be `GPIO_ACTIVE_HIGH`, and interrupt pins set in `interrupt-gpios` should have the flags `(GPIO_ACTIVE_HIGH | GPIO_PULL_DOWN)`.

## Composite Driver

Keyboard scan driver which combines multiple other keyboard scan drivers.

### Devicetree

Applies to : `compatible = "zmk,kscan-composite"`

Definition file: [zmk/app/dts/bindings/zmk,kscan-composite.yaml](https://github.com/zmkfirmware/zmk/blob/main/app/dts/bindings/zmk,kscan-composite.yaml)

| Property  | Type | Description                                   | Default |
| --------- | ---- | --------------------------------------------- | ------- |
| `rows`    | int  | The number of rows in the composite matrix    |         |
| `columns` | int  | The number of columns in the composite matrix |         |

The `zmk,kscan-composite` node should have one child node per keyboard scan driver that should be composited. Each child node can have the following properties:

| Property     | Type    | Description                                                                    | Default |
| ------------ | ------- | ------------------------------------------------------------------------------ | ------- |
| `kscan`      | phandle | Label of the kscan driver to include                                           |         |
| `row-offset` | int     | Shifts row 0 of the included driver to a new row in the composite matrix       | 0       |
| `col-offset` | int     | Shifts column 0 of the included driver to a new column in the composite matrix | 0       |

### Example Configuration

For example, consider a macropad with a 3x3 matrix and two direct GPIO keys:

<div style={{columns: 2, marginBottom: '1em'}}>
<div style={{breakInside: 'avoid'}}>
Matrix:

<table>
    <thead>
        <tr><th></th><th>Col 0</th><th>Col 1</th><th>Col 2</th></tr>
    </thead>
    <tbody>
        <tr><th>Row 0</th><td>A0</td><td>A1</td><td>A2</td></tr>
        <tr><th>Row 1</th><td>A3</td><td>A4</td><td>A5</td></tr>
        <tr><th>Row 2</th><td>A6</td><td>A7</td><td>A8</td></tr>
    </tbody>
</table>
</div>

<div style={{breakInside: 'avoid'}}>
Direct GPIO:

<table>
    <thead>
        <tr><th></th><th>Col 0</th><th>Col 1</th></tr>
    </thead>
    <tbody>
        <tr><th>Row 0</th><td>B0</td><td>B1</td></tr>
    </tbody>
</table>
</div>
</div>

To combine them, we need to create a composite matrix with enough rows and columns to fit both sets of keys without overlapping, then set row and/or columns offsets to shift them so they do not overlap.

One possible way to do this is a 3x4 matrix where the direct GPIO keys are shifted to below the matrix keys...

<table>
    <thead>
        <tr><th></th><th>Col 0</th><th>Col 1</th><th>Col 2</th></tr>
    </thead>
    <tbody>
        <tr><th>Row 0</th><td>A0</td><td>A1</td><td>A2</td></tr>
        <tr><th>Row 1</th><td>A3</td><td>A4</td><td>A5</td></tr>
        <tr><th>Row 2</th><td>A6</td><td>A7</td><td>A8</td></tr>
        <tr><th>Row 3</th><td>B0</td><td>B1</td><td>(none)</td></tr>
    </tbody>
</table>

...which can be configured with the following Devicetree code:

```dts
/ {
    chosen {
        zmk,kscan = &kscan0;
    };

    kscan0: kscan_composite {
        compatible = "zmk,kscan-composite";
        rows = <4>;
        columns = <3>;

        // Include the matrix driver
        matrix {
            kscan = <&kscan1>;
        };

        // Include the direct GPIO driver...
        direct {
            kscan = <&kscan2>;
            row-offset = <3>; // ...and shift it to not overlap
        };
    };

    kscan1: kscan_matrix {
        compatible = "zmk,kscan-gpio-matrix";
        // define 3x3 matrix here...
    };

    kscan2: kscan_direct {
        compatible = "zmk,kscan-gpio-direct";
        // define 2 direct GPIOs here...
    };
}
```

## Mock Driver

Mock keyboard scan driver that simulates key events.

### Devicetree

Applies to: `compatible = "zmk,kscan-mock"`

Definition file: [zmk/app/dts/bindings/zmk,kscan-mock.yaml](https://github.com/zmkfirmware/zmk/blob/main/app/dts/bindings/zmk%2Ckscan-mock.yaml)

| Property       | Type  | Description                                   | Default |
| -------------- | ----- | --------------------------------------------- | ------- |
| `event-period` | int   | Milliseconds between each generated event     |         |
| `events`       | array | List of key events to simulate                |         |
| `rows`         | int   | The number of rows in the composite matrix    |         |
| `columns`      | int   | The number of columns in the composite matrix |         |
| `exit-after`   | bool  | Exit the program after running all events     | false   |

The `events` array should be defined using the macros from [app/module/include/dt-bindings/zmk/kscan_mock.h](https://github.com/zmkfirmware/zmk/blob/main/app/module/include/dt-bindings/zmk/kscan_mock.h).

## Kscan Sideband Behavior Driver

The Kscan sideband behaviors node can be used to assign behaviors to keys in a manner distinctly separate from the keymap. These assignments and definitions will not be affected by nor have any effect on the keymap.

### Devicetree

Applies to: `compatible = "zmk,kscan-sideband-behaviors"`

Definition file: [zmk/app/dts/bindings/kscan/zmk,matrix-transform.yaml](https://github.com/zmkfirmware/zmk/blob/main/app/dts/bindings/kscan/zmk%2Ckscan-sideband-behaviors.yaml)

| Property        | Type    | Description                                               |
| --------------- | ------- | --------------------------------------------------------- |
| `kscan`         | phandle | Phandle to a kscan containing keys to assign behaviors to |
| `auto-enable`   | bool    | Enables the sideband instance on startup unconditionally  |
| `wakeup-source` | bool    | Mark this kscan instance as able to wake the keyboard     |

If `auto-enable` is not set, then the sideband behavior will wait for an external activation source before being enabled, e.g. being assigned as the chosen `zmk,kscan`. The `kscan` can contain additional keys, which will be used by the keymap if this node is set as the chosen `zmk,kscan` and has an appropriate matrix transformation defined.

Each child node should have the following properties:

| Property   | Type          | Description                                                                           | Default |
| ---------- | ------------- | ------------------------------------------------------------------------------------- | ------- |
| `row`      | int           | The row index of the key in the `kscan` to intercept and trigger a behavior for       | 0       |
| `column`   | int           | The column index of the key in the `kscan` to intercept and trigger a behavior for    |         |
| `bindings` | phandle-array | The behavior that should be triggered when the matching row and column event triggers |         |
