Updated FAQ (markdown)

FAQ.md

@@ -154,6 +154,11 @@ This LED can be very distracting. Unfortunately it can't easily be disabled as i
 
 Although pins D1 and D2 are usually regarded the best GPIO pins to use in an ESP8266 project, D4 is the default in WLED, despite having two major and one minor drawback. The major drawbacks are the permanently lit blue onboard LEDs and the fact that the pin level needs to be high (pullup) at powerup or the controller will not boot. A minor drawback is that the `Serial1` bus can not be used, but this is irrelevant in most cases, as the USB/serial converter is connected to the other `Serial` interface. The reason for using this pin is that it uses UART hardware driving, which increases stability and decreases CPU overhead especially with larger amounts of pixels.
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+<summary>Why can I only use 500 LEDs on the ESP8266 GPIO pin 3?</summary>
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+The problem is the DMA hardware driving method used on (just) that pin. It works well, but uses **4x (!)** as much RAM memory as the UART hardware driving on pin 2 and the bitbang driver on all other pins.
    
 ## General Questions