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torvalds
GitHub Repository: torvalds/linux
 Path: blob/master/Documentation/devicetree/bindings/input/gpio-charlieplex-keypad.yaml
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# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)

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%YAML 1.2

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---

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$id: http://devicetree.org/schemas/input/gpio-charlieplex-keypad.yaml#

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$schema: http://devicetree.org/meta-schemas/core.yaml#

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title: GPIO charlieplex keypad

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maintainers:

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  - Hugo Villeneuve <hvilleneuve@dimonoff.com>

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description: |

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  The charlieplex keypad supports N^2)-N different key combinations (where N is

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  the number of I/O lines). Key presses and releases are detected by configuring

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  only one line as output at a time, and reading other line states. This process

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  is repeated for each line. Diodes are required to ensure current flows in only

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  one direction between any pair of pins, as well as pull-up or pull-down

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  resistors on all I/O lines.

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  This mechanism doesn't allow to detect simultaneous key presses.

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  Wiring example for 3 lines keyboard with 6 switches and 3 diodes (pull-up/down

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  resistors not shown but needed on L0, L1 and L2):

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  L0  --+---------------------+----------------------+

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        |                     |                      |

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  L1  -------+-----------+---------------------+     |

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        |    |           |    |                |     |

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  L2  -------------+----------------+-----+    |     |

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        |    |     |     |    |     |     |    |     |

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        |    |     |     |    |     |     |    |     |

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        |  S1 \  S2 \    |  S3 \  S4 \    |  S5 \  S6 \

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        |    |     |     |    |     |     |    |     |

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        |    +--+--+     |    +--+--+     |    +--+--+

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        |       |        |       |        |       |

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        |    D1 v        |    D2 v        |    D3 v

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        |       - (k)    |       - (k)    |       - (k)

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        |       |        |       |        |       |

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        +-------+        +-------+        +-------+

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  L: GPIO line

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  S: switch

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  D: diode (k indicates cathode)

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allOf:

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  - $ref: input.yaml#

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  - $ref: /schemas/input/matrix-keymap.yaml#

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properties:

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  compatible:

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    const: gpio-charlieplex-keypad

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  autorepeat: true

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  debounce-delay-ms:

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    default: 5

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  line-gpios:

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    description:

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      List of GPIOs used as lines. The gpio specifier for this property

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      depends on the gpio controller to which these lines are connected.

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  linux,keymap: true

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  poll-interval: true

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  settling-time-us: true

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  wakeup-source: true

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required:

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  - compatible

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  - line-gpios

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  - linux,keymap

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  - poll-interval

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additionalProperties: false

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examples:

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  - |

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    #include <dt-bindings/gpio/gpio.h>

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    #include <dt-bindings/input/input.h>

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    keyboard {

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        compatible = "gpio-charlieplex-keypad";

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        debounce-delay-ms = <20>;

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        poll-interval = <5>;

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        settling-time-us = <2>;

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        line-gpios = <&gpio2 25 (GPIO_ACTIVE_HIGH | GPIO_PULL_DOWN)

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                      &gpio2 26 (GPIO_ACTIVE_HIGH | GPIO_PULL_DOWN)

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                      &gpio2 27 (GPIO_ACTIVE_HIGH | GPIO_PULL_DOWN)>;

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        /* MATRIX_KEY(output, input, key-code) */

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        linux,keymap = <

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            /*

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             * According to wiring diagram above, if L1 is configured as

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             * output and HIGH, and we detect a HIGH level on input L0,

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             * then it means S1 is pressed: MATRIX_KEY(L1, L0, KEY...)

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             */

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            MATRIX_KEY(1, 0, KEY_F1) /* S1 */

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            MATRIX_KEY(2, 0, KEY_F2) /* S2 */

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            MATRIX_KEY(0, 1, KEY_F3) /* S3 */

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            MATRIX_KEY(2, 1, KEY_F4) /* S4 */

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            MATRIX_KEY(1, 2, KEY_F5) /* S5 */

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            MATRIX_KEY(0, 2, KEY_F6) /* S6 */

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        >;

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    };

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