Mode-S Beast:DIP Switches

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Mode-S Beast DIP-Switches

The 10 DIP switches on the component side of the PCB. Remove the brown protection with a sharp knife.

There are 10 DIP switches plus 6 solder jumpers used for configuring various optional functions of the Mode-S Beast. Currently not all of them are used and so foreseen to further extensions.

On HW V1.0 (sold around May 2011), at minimum one solder jumper is always needed at the TX-Data multiplexer:
In most cases it is the solder jumper named USB, which connects the serial output of the FPGA to the USB interface. The other possible selections are Xport (Xp) and BlueTooth (BT). Multiple connections are possible for TX-Data. The default configuration for USB is normally done before shipping.

The fallback position of the DIP switches is all off, means towards the LED: 3MBit/sec over USB, no special function activated. In case of problems with the Mode-S Beast, I always suggest falling back to this setting.

DIP Switches in the Short

DIP Function (if set to ON) Recommened Setting
1,2 Baudrate between FPGA and USB interface both OPEN
3 FW <=V1.21: AVR Format for transmission over Ethernet
FW >= V1.30: Binary Format
FW <=V1.21: OPEN
FW >=V1.30: ON
4 DF11/17 filter: The Mode-S Beast only decodes DF-11, DF-17 and DF-18 frames OPEN
5 MLAT timestamp enable ON
6 CRC check disable (for DF-11 and DF-17) OPEN (*1)
7 DF-0/4/5 filter: The Mode-S Beast does not decode those types
(mostly used when having performance problems)
8 RTS handshake enable ON
(see note below)
9 1 bit forward error correction disable OPEN (*2)
10 Mode-A/C decoding enable ON

(*1) Only then use DIP#6 ON position if you really know what it does.

(*2) 1 bit FEC may cause some spurious decodes of non existing aircraft because the safety of the CRC is decreased with it. If you are feeding databases, sharing networks or similar, and if this is a matter for you, disable FEC (DIP#9=ON). Otherwise, if you are just watching the air traffic, keep this switch in OPEN position in order to have as many frames as possible. Those just watching would never recognize but enjoy a bigger number of frames beeing received and enjoy some smoother traces.
Technical note: The Mode-S documents speak about even up to 5 bits beeing correctible, but when I once tried a 3 bit error correction, there were so many spuriouses that even just watching was not a pleasure. I have no idea how a true good/bad decision on these frames can be made successfully in order to make use of them.

DIP Switches in Detail

Baudrate SW1 SW2 Usage
3 MBit/sec (*3) open open USB serial interface (with USB over FT232R only)
921600 Bit/sec (*4) closed open Bluetooth interface, Lantronix Xport (Xport needs to be set to high performance mode)
230400 Bit/sec open closed
115200 Bit/sec closed closed

(*3) Until FW version V1.15 this baudrate was 1MBit/sec. It became changed to 3MBit/sec with FW Version V1.21 and later (*4) This setting can be used when operating USB and Ethernet in parallel

Note that depending on your local traffic rate the interface baudrate is the real bottleneck of your system! So if you see a significant miss here, first introduce the DF-0/4/5 filter with DIP #7, and if that does not help, switch on DF17/DF11 filter with DIP#4. See also my comment here.

The Mode-S frames capability of the different baudrates is about:

Baudrate Estimated number of Mode-S
frames per second maximum
in UDP format
Estimated number of Mode-S
frames per second maximum
in binary format
3 MBit more than 2000 more than 4000
921600 Bit/sec 1100 2200
230400 Bit/sec 550 1100
115200 Bit/sec 300 150

These are very rougth estimations!!!
Mode-AC frames are output with lower priority, so if your interface is already conguested with Mode-S frames, you will see less or no Mode-AC frames.

Planeplotter UDP Input Format
FW V1.21 and earlier (mostly obsolete)
SW3 Usage (see also output formats page)
disabled open Standard output:

56 Bit Mode-S frames: *02E99619FACDAE;
112 Bit Mode-S frames: *8D3C5EE69901BD9540078D37335F;
Mode-A/C frames: *7700;

(Mode-A/C frame values are octal)

With MLAT information:

56 Bit Mode-S frames: @016CE3671C745DFFE7AB7BFCAB;
112 Bit Mode-S frames: @016CE3671AA88D00199A8BB80030A8000628F400;
Mode-A/C frames: @016CE3671C747700;

(Mode-A/C frame values are octal)

The distinction between Mode-S and Mode-A/C is done using the length of the frame.
enabled closed Only necessary/used if

1) Lantronix Xport is used for network data transfer AND
2) UDP data transfer towards Planeplotter is used

(there is also a COM port emulation for the Lantronix Xport, using TCP/IP between the Xport and the computer, which does not need the 'AV' prefix)

Planeplotter then needs a prefix 'AV' in order to distinguish the data from other network data.

Standard output:


With MLAT information:</br>
Output Binary format
FW V1.30 and later
SW3 Usage (see also output formats page)
AVR Format open The output is in AVR format, see above in "open" position
Binary Format closed The output is done in binary format, including signal level information.
This is the recommended mode when connecting the Mode-S Beast via Ethernet to Planeplotter.
DF-11/DF-17/18 only SW4 Usage
all standard data formats open The Mode-S beast will decode all data formats that are currently used:
DF-0, DF-4, DF-5, DF-11, DF-16, DF-17, DF-18, DF20 and DF-21
Note: DF-0, DF-4 and DF-5 can be masked with DIP#7
only DF-17 frames closed Only DF-17 or DF-11 frames are decoded. This can be used for example if you experience severe performance problems on the serial interface.
MLAT enable SW5 Usage
MLAT information off open AVR format only: No MLAT information is provided, data frames are initiated with '*'
MLAT information on closed AVR format only: MLAT information is provided using a 12MHz (83ns resolution), all frames are initiated with '@'.
Note: The binary format always contains MLAT information.
CRC disable SW6 Usage
CRC on DF-11, DF-17, DF-18 open DF-17 frames are checked for a total match of the CRC DF-11 frames are checked for all but the lower 6/7 bits, which are the Interrogator ID and not usable for checking
no CRC check closed No CRC check is done for any frame. This can be used in conjunction with the CRC and biterror correction PC software driver or Planeplotter's FEC correction in order to get a higher frame rate.
Important Note: I do not know from which sources, but there are some which are telling having DIP#6 in "ON" position. This quickly leads into interface overload. It is recommended for only for special use.
DF-0/DF-4/DF-5 filter SW7 Usage
not active open If your setup is able to handle high load, this selection should be used
filter all DF-0, DF-4 and DF-5 frames closed These frame types are the ones with least useful information and so they should be the first ones that can be masked in case of interface or Planeplotter processsing overload.
RTS Handshake enable SW8 Usage
Hardware handshake
open Only recommended with GUI software that does not enable hardware handshake.
Hardware handshake
closed Always recommended.
Note: This handshake is acutally not done between the GUI and the FPGA, much better it is done exactly between the interface device and the FPGA.

The reason why this DIP is in OPEN in delivery state is that the Beast always should output data, disregarding any handshake setting. I am simply afraid of too many users that come back with the note "The Beast does not output data...." just because of this small DIP. After having seen that the Beast works, please enable RTS handshake and see that it still works.

1 Bit FEC disable SW9 Usage
Forward error correction
open The CRC checksum of Mode-S frames allows a correction of up to 5 bits. 1 Bit errors are those appearing most often and are corrected with this feature by the Mode-S Beast for DF-11 and DF-17/DF-18 frames
Forward error correction
closed There is no bit error correction done in the Mode-S Beast.
Important Note: Since FEC lowers the error detection rate by nature, those users feeding databases or sharing networks that observe every single occurance of ICAO IDs, may decide having FEC disabled. Such users that only watch traffic as a spotter should turn FEC on for a maximum frame rate.
Mode-A/C frame decoding SW10 Usage
disabled open No Mode-A/C frames are decoded by the Mode-S Beast
enabled closed Mode-S Beast also decodes Mode-A/C frames Frame format, see DIP#3