# Receivers (RX)

A receiver is used to receive radio control signals from your transmitter and convert them into signals that the flight controller can understand.

There are 3 basic types of receivers:

Parallel PWM Receivers
PPM Receivers
Serial Receivers

## Parallel PWM Receivers

8 channel support, 1 channel per input pin.  On some platforms using parallel input will disable the use of serial ports
and SoftSerial making it hard to use telemetry or GPS features.

## PPM Receivers

PPM is sometimes known as PPM SUM or CPPM.

12 channels via a single input pin, not as accurate or jitter free as methods that use serial communications, but readily available.

These receivers are reported working:

FrSky D4R-II
http://www.frsky-rc.com/product/pro.php?pro_id=24

Graupner GR24
http://www.graupner.de/en/products/33512/product.aspx

## Serial Receivers

### Spektrum

8 channels via serial currently supported.

These receivers are reported working:

Lemon Rx DSMX Compatible PPM 8-Channel Receiver + Lemon DSMX Compatible Satellite with Failsafe
http://www.lemon-rx.com/shop/index.php?route=product/product&product_id=118


### S.BUS

16 channels via serial currently supported.

These receivers are reported working:

FrSky X4RSB 3/16ch Telemetry Receiver
http://www.frsky-rc.com/product/pro.php?pro_id=135

#### OpenTX S.BUS configuration

If using OpenTX set the transmitter module to D16 mode and select CH1-16 on the transmitter before binding to allow reception
of 16 channels. 

OpenTX 2.09, which is shipped on some Taranis X9D Plus transmitters, has a bug - [issue:1701](https://github.com/opentx/opentx/issues/1701).
The bug prevents use of all 16 channels.  Upgrade to the latest OpenTX version to allow correct reception of all 16 channels,
without the fix you are limited to 8 channels regardless of the CH1-16/D16 settings.


### XBUS

The firmware currently supports the MODE B version of the XBus protocol.
Make sure to set your TX to use "MODE B" for XBUS in the TX menus!
See here for info on JR's XBUS protocol: http://www.jrpropo.com/english/propo/XBus/

These receivers are reported working:

XG14 14ch DMSS System w/RG731BX XBus Receiver
http://www.jramericas.com/233794/JRP00631/

### SUMD

16 channels via serial currently supported.

These receivers are reported working:

GR-24 receiver HoTT
http://www.graupner.de/en/products/33512/product.aspx

Graupner receiver GR-12SH+ HoTT
http://www.graupner.de/en/products/870ade17-ace8-427f-943b-657040579906/33565/product.aspx

### SUMH

8 channels via serial currently supported.

SUMH is a legacy Graupner protocol.  Graupner have issued a firmware updates for many recivers that lets them use SUMD instead.

## MultiWii serial protocol (MSP)

Allows you to use MSP commands as the RC input.  Only 8 channel support to maintain compatibility with MSP.
 
## Configuration

There are 3 features that control receiver mode:

```
RX_PPM
RX_SERIAL
RX_PARALLEL_PWM
RX_MSP
```

Only one receiver feature can be enabled at a time.

### Serial RX

See the Configuration document some some RX configuration examples.

For Serial RX enable `RX_SERIAL` and set the `serialrx_provider` CLI setting as follows.

| Serial RX Provider | Value |
| ------------------ | ----- |
| SPEKTRUM1024       | 0     |
| SPEKTRUM2048       | 1     |
| SBUS               | 2     |
| SUMD               | 3     |
| SUMH               | 4     |
| XBUS_MODE_B        | 5     |


### PPM/PWM input filtering.

Hardware input filtering can be enabled if you are experiencing interference on the signal sent via your PWM/PPM RX.

Use the `input_filtering_mode` CLI setting to select a mode.

| Value | Meaning   |
| ----- | --------- |
| 0     | Disabled  |
| 1     | Enabled   |