<p>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.</p>
<hr />
<p>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.</p>
<p><a href="https://i.sstatic.net/3fuAH.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/3fuAH.png" alt="enter image description here" /></a></p>
<p>The FS-iA6B has three different major output modes:</p>
<ul>
<li>PWM: Each channel (<em>1-6</em>) is output on its own servo channel</li>
<li>PPM: Each channel (<em>I think either 1-8 or 1-10</em>) is output sequentially on one servo channel in accordance with the <a href="https://github.com/claymation/CPPM" rel="nofollow noreferrer">CPPM (<em>combined PPM</em>) protocol</a>
<ul>
<li>If enabled, CPPM is output on the <code>PPM/CH1</code> servo channel</li>
</ul>
</li>
<li>iBUS: Each channel is output over a serial UART connection
<ul>
<li>If enabled, serial iBUS is output on the <code>PPM/CH1</code> servo channel</li>
<li>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.</li>
</ul>
</li>
</ul>
<p>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.</p>

CC BY-SA 4.0
2020-11-06T18:26:50.263Z
so it should work just the same as a receiver with 3 pins?
Ceramicmrno0b
CC BY-SA 4.0
2020-11-06T18:27:20.153Z
Well, what do you mean by that? Which receiver with 3 pins matters a lot! :)
ifconfig
CC BY-SA 4.0
2020-11-06T18:29:10.060Z
This is a [link](https://www.banggood.com/JJRC-JJPRO-EM-16-2_4GHz-6CH-AFHDS-2A-Mode-2-RC-Transmitter-with-Receiver-Support-P175-for-RC-Drone-p-1724957.html?rmmds=search&cur_warehouse=CN) to the receiver I need to replace.
Ceramicmrno0b
CC BY-SA 4.0
2020-11-06T18:30:58.113Z
Oh! So you mean will the PWM outputs work identically? Yes, they will function the same.
ifconfig
CC BY-SA 4.0
2020-11-06T18:35:30.007Z
good to know, thanks!
Ceramicmrno0b
CC BY-SA 4.0
2020-11-09T09:12:09.793Z
In case it's not  obvious, the main advantage of iBus or CPPM is that you only need one cable when sending the signal to a flight controller. Also, is the 'sens' socket input for telemetry?
Robin Bennett
CC BY-SA 4.0
2020-11-06T18:17:31.830Z
2020-11-06T18:31:59.897Z
2020-11-06T18:31:59.897Z
ifconfig
<p>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.</p>
<p>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?</p>
<p><a href="https://rads.stackoverflow.com/amzn/click/com/B07D35C6MQ" rel="noreferrer" rel="nofollow noreferrer">Receiver with 4th line of pins</a></p>

<receiver>
What is this 4th row of pins on some receivers?
Ceramicmrno0b
# What is this 4th row of pins on some receivers?

(Asked by: username_0 on 2020-11-06)

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](https://rads.stackoverflow.com/amzn/click/com/B07D35C6MQ)

**Tags:** receiver

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## 1 answers

### Answer by username_1 on 2020-11-06. Score: 4 | Accepted 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.

[![enter image description here](https://i.sstatic.net/3fuAH.png)](https://i.sstatic.net/3fuAH.png)

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](https://github.com/claymation/CPPM)
  + 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 "analog" ones.

> **Comments:**
> **username_0**: so it should work just the same as a receiver with 3 pins?  
> **username_1**: Well, what do you mean by that? Which receiver with 3 pins matters a lot! :)  
> **username_0**: This is a [link](https://www.banggood.com/JJRC-JJPRO-EM-16-2_4GHz-6CH-AFHDS-2A-Mode-2-RC-Transmitter-with-Receiver-Support-P175-for-RC-Drone-p-1724957.html?rmmds=search&cur_warehouse=CN) to the receiver I need to replace.  
> **username_1**: Oh! So you mean will the PWM outputs work identically? Yes, they will function the same.  
> **username_0**: good to know, thanks!  
> **username_2**: In case it's not  obvious, the main advantage of iBus or CPPM is that you only need one cable when sending the signal to a flight controller. Also, is the 'sens' socket input for telemetry?  

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