title_body: What is this 4th row of pins on some receivers? I was looking for a new receiver(think I fried mine) and noticed that some receivers have a 4th line of pins. I've only seen this on receivers where the connections are on the side instead of the top.
  What does this 4th line of pins do? Will it work for my plane just the same as a receiver with only three pins? Is there a reason they only appear when the connections are on the side?
  Receiver with 4th line of pins
upvoted_answer: Modern RC receivers that support PWM/servo output will also support other output modes, which is what the fourth row of pins are usually for.
  
  The extra row of pins you notice on the FlySky FS-iA6B receiver is for extra features of the iBUS signal output. The regular three-high 6-channel PWM outputs are present too.
  
  The FS-iA6B has three different major output modes:
  
  PWM: Each channel (1-6) is output on its own servo channel
  PPM: Each channel (I think either 1-8 or 1-10) is output sequentially on one servo channel in accordance with the CPPM (combined PPM) protocol
  
  If enabled, CPPM is output on the PPM/CH1 servo channel
  
  
  iBUS: Each channel is output over a serial UART connection
  
  If enabled, serial iBUS is output on the PPM/CH1 servo channel
  Special auxilary features of the iBUS protocol are available on the 4th row of pins, but these are rarely used. The iBUS signal channel provides all the features usually required fy RC aircraft.
  
  
  
  Of the three, iBUS is preferred for use with modern hardware if its supported because of the error-resistant and precision qualities of digital signaling protocols over &quot;analog&quot; ones.