2020 February 29 Breaking Changes Update (#8064)

[jackhill/qmk/firmware.git] / docs / feature_backlight.md

diff --git a/docs/feature_backlight.md b/docs/feature_backlight.md
index e74aab1..7c68d74 100644 (file)
--- a/docs/feature_backlight.md
+++ b/docs/feature_backlight.md
@@ -119,10 +119,22 @@ When both timers are in use for Audio, the backlight PWM will not use a hardware
 
 To change the behavior of the backlighting, `#define` these in your `config.h`:
 
-|Define               |Default      |Description                                                                                                   |
-|---------------------|-------------|--------------------------------------------------------------------------------------------------------------|
-|`BACKLIGHT_PIN`      |`B7`         |The pin that controls the LEDs. Unless you are designing your own keyboard, you shouldn't need to change this |
-|`BACKLIGHT_PINS`     |*Not defined*|experimental: see below for more information                                                                  |
+|Define               |Default      |Description                                                                                                  |
+|---------------------|-------------|-------------------------------------------------------------------------------------------------------------|
+|`BACKLIGHT_PIN`      |`B7`         |The pin that controls the LEDs. Unless you are designing your own keyboard, you shouldn't need to change this|
+|`BACKLIGHT_PINS`     |*Not defined*|experimental: see below for more information                                                                 |
+|`BACKLIGHT_LEVELS`   |`3`          |The number of brightness levels (maximum 31 excluding off)                                                   |
+|`BACKLIGHT_CAPS_LOCK`|*Not defined*|Enable Caps Lock indicator using backlight (for keyboards without dedicated LED)                             |
+|`BACKLIGHT_BREATHING`|*Not defined*|Enable backlight breathing, if supported                                                                     |
+|`BREATHING_PERIOD`   |`6`          |The length of one backlight "breath" in seconds                                                              |
+|`BACKLIGHT_ON_STATE` |`1`          |The state of the backlight pin when the backlight is "on" - `1` for high, `0` for low                        |
+
+### Backlight On State
+
+Most backlight circuits are driven by an N-channel MOSFET or NPN transistor. This means that to turn the transistor *on* and light the LEDs, you must drive the backlight pin, connected to the gate or base, *high*.
+Sometimes, however, a P-channel MOSFET, or a PNP transistor is used. In this case, when the transistor is on, the pin is driven *low* instead.
+
+This functionality is configured at the keyboard level with the `BACKLIGHT_ON_STATE` define.
 
 ### Multiple backlight pins