qmk-firmware/keyboards/centromere/keymaps/default_u2/keymap.c

#include QMK_KEYBOARD_H

enum centromere_layers
{
	_STD,
	_NUM,
	_FN
};

const uint16_t PROGMEM keymaps[][MATRIX_ROWS][MATRIX_COLS] = {

  [_STD] = LAYOUT_split_3x6_3( \
  //,-----------------------------------------------------.                    ,-----------------------------------------------------.
       KC_TAB,    KC_Q,    KC_W,    KC_E,    KC_R,    KC_T,                         KC_Y,    KC_U,    KC_I,    KC_O,   KC_P,  KC_BSPC,\
  //|--------+--------+--------+--------+--------+--------|                    |--------+--------+--------+--------+--------+--------|
      KC_LCTL,    KC_A,    KC_S,    KC_D,    KC_F,    KC_G,                         KC_H,    KC_J,    KC_K,    KC_L, KC_SCLN, KC_QUOT,\
  //|--------+--------+--------+--------+--------+--------|                    |--------+--------+--------+--------+--------+--------|
      KC_LSFT,    KC_Z,    KC_X,    KC_C,    KC_V,    KC_B,                         KC_N,    KC_M, KC_COMM,  KC_DOT, KC_SLSH,  KC_ENT,\
  //|--------+--------+--------+--------+--------+--------+--------|  |--------+--------+--------+--------+--------+--------+--------|
                                          KC_LGUI, MO(_FN),  KC_SPC,     KC_SPC,MO(_NUM),  KC_RALT \
                                      //`--------------------------'  `--------------------------'

  ),


  [_NUM] = LAYOUT_split_3x6_3( \
  //,-----------------------------------------------------.                    ,-----------------------------------------------------.
       KC_ESC,    KC_1,    KC_2,    KC_3,    KC_4,    KC_5,                         KC_6,    KC_7,    KC_8,    KC_9,    KC_0, KC_BSPC,\
  //|--------+--------+--------+--------+--------+--------|                    |--------+--------+--------+--------+--------+--------|
        KC_F1,   KC_F2,   KC_F3,   KC_F4,   KC_F5,   KC_F6,                        KC_F7,   KC_F8,   KC_F9,  KC_F10,  KC_F11,  KC_F12,\
  //|--------+--------+--------+--------+--------+--------|                    |--------+--------+--------+--------+--------+--------|
      KC_LSFT, XXXXXXX, XXXXXXX, XXXXXXX, XXXXXXX, XXXXXXX,                      XXXXXXX, KC_LEFT, KC_DOWN,   KC_UP,KC_RIGHT,  KC_ENT,\
  //|--------+--------+--------+--------+--------+--------+--------|  |--------+--------+--------+--------+--------+--------+--------|
                                          KC_LGUI, MO(_FN),  KC_SPC,     KC_ENT,MO(_NUM), KC_RALT \
                                      //`--------------------------'  `--------------------------'
    ),

  [_FN] = LAYOUT_split_3x6_3( \
  //,-----------------------------------------------------.                    ,-----------------------------------------------------.
       KC_ESC, KC_EXLM,   KC_AT, KC_HASH,  KC_DLR, KC_PERC,                      KC_CIRC, KC_AMPR, KC_ASTR, KC_LPRN, KC_RPRN, KC_BSPC,\
  //|--------+--------+--------+--------+--------+--------|                    |--------+--------+--------+--------+--------+--------|
      KC_LCTL,   KC_F2,   KC_F3,   KC_F4,   KC_F5,   KC_F6,                      KC_MINS,  KC_EQL, KC_LCBR, KC_RCBR, KC_PIPE,  KC_GRV,\
  //|--------+--------+--------+--------+--------+--------|                    |--------+--------+--------+--------+--------+--------|
      KC_LSFT, XXXXXXX, XXXXXXX, XXXXXXX, XXXXXXX, XXXXXXX,                      KC_UNDS, KC_PLUS, KC_LBRC, KC_RBRC, KC_BSLS, KC_TILD,\

                                          KC_LGUI, MO(_FN),  KC_SPC,     KC_ENT,MO(_NUM), KC_RALT \
                                      //`--------------------------'  `--------------------------'
  ),

};

void matrix_scan_user(void) {
    uint8_t layer = get_highest_layer(layer_state);

    switch (layer) {
    	case _STD:
    		set_led_off;
    		break;
        case _FN:
            set_led_blue;
            break;
        case _NUM:
            set_led_red;
            break;
        default:
            break;
    }
};