2015/07/23 00:16
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Virtually all of the inofrmation in this document was provided by hammer22.  So Thanks!


DSM2 data packets consist of 7 channels each.  the packets are formatted as 16bit MSB-1st values

Data can be either 10 or 11 bits.

6-channel DSM2 = 10bit

8-channel DSM2 = 11bit

All DSMx appears to be 11bit

A packet consists of a Tx ID + upto 7 channels of data

each 16bit data value is defined as:


a 0 bbbb cccccccccc


a bbbb  ccccccccccc

a:    0 for 1st data packet, 1 for 1st channel in 2nd data packet

bbbb: the channel number of this packet

cc..: 10 or 11bit channel data (MSB 1st)

The channel data will be 0xffff if the specific channel slot is unused

Channel assignment appears to be:

0: Throttle

1: Aileron

2: Elevator

3: Rudder

4: Gear

5: Aux1

6: Aux2

7: Aux3

Data packets are defined as:

aa bb cccc dddd eeee ffff gggg hhhh iiii

aa: If DSM2: 0xff - mfgid[2], if DSMX mfgid[2]

bb: If DSM2: 0xff - mfgid[3] + offset, if DSMX mfgid[3] + offset (see binding)

cccc: Channel

dddd: Channel

eeee: Channel

ffff: Channel

gggg: Channel

hhhh: Channel

iiii: Channel

Each packet is sent twice, once on channel 'a' and 4msec later on channel 'b'

If there are more than 7 channels to transmit, the upper channels are transmitted using the same

packet format 11mec after the the low-channel packet.

New channel data is transmitted each 22msec

For example:

 0msec: Transmit channels 0-7 on channel 'a'

 4msec: Transmit channels 0-7 on channel 'b'

11msec: Transmit channels 8-14 on channel 'a'

15msec: Transmit channels 8-14 on channel 'b'

22msec: Transmit channels 0-7 on channel 'a'

New SOP(8 bytes) and Data (16 bytes) codes are sent before each packet.


The bind packet is as follows:

aa bb cc dd aa bb cc dd eeee ff gg hh ii jjjj

aa   : 0xff - mfgid[0]

bb   : 0xff - mfgid[1]

cc   : 0xff - mfgid[2]

dd   : 0xff - mfgid[3] + offset

eeee : 384 + sum of bytes 0 through 7

ff   : Unknown (value = 0x01)

gg   : # of channels being transmitted

hh   : Transmitter capabilities

     : HP6DSM (DSM2): 0x01

     : DX6i   (DSMX): 0xA2

     : DX8    (DSM2): 0x12

     : DX8    (DSMX): 0xB2

     : DM9    (DSM2): 0x02

# of packets (1 if num-channels < 8, 2 if num-channels >= 8) for DSM2

ii   : Unknown (value = 0x00)

jjjj : eeee + sum of bytes 8 through 13

The bind channel can be any odd channel between 0x01 and 0x4f

The SOP and CRC are set as below for the chosen bind channel

the DATA code is 32 bytes.  The 1st 16 bytes are as defined below for the bind channel.

The 2nd 16 bytes are always:

D7A154B15E89AE86 C69422FE48E6574E

Once the Rx detectes that the bind packet is no longer being sent, it

will transmit a confirmation on the same channel using the fillowing 16byte DATA code:

98881BE430790384 060C12181E247110

It is not required that the Tx receives or acts upon this packet

The confirmation data is:

aa bb cc dd ee ff gg hh ii jj

aa: byte[0] of bind packet

bb: byte[1] of bind packet

cc: byte[2] of bind packet

dd: byte[3] of bind packet

ee: byte[10] of bind packet (always 0x01)

ff: # of supported channels(?)

    AR7000=0x07, AR6010=0x07, AR6210=0x07

gg: requested packet type

    AR6210 connected to HP6DSM(DSM2): 0x01 (DSM2 requested)

    AR7000 connected to DX6i (DSMX):  0x01 (DSM2 requested)

    AR6010 connected to DX6i (DSMX):  0xA2 (DSMX requested)

hh: byte[13] of bind packet (always 0x00)

SOP/Data/CRC code selection:

there is one set of SOP, Data, and CRC codes for each transmit channel.

The SOP and DATA codes come from the Cypress recommended SOP table.  the codes are documented here:


They are organized in 5 rows of 9 columns with the contenst of each 'cell' being an 8-byte PN code

The row is determined by the transmit channel as:

row = channel modulo 5

The columns are determined from the mfgid as follows:

sop-col = (mfgid[0] + mfgid[1] + mfgid[2] + 2) & 0x07

data-col0 = 7 - sop-col

data-col1 = data-col0 + 1

The crc for channel 'a' is NOT(mfgid[1] << 8 + mfgid[0])

The crc for channel 'b' is (mfgid[1] << 8 + mfgid[0])

Here is the table (note that I've transposed rows and columns to make it easier to read)

Note: Values are LSB 1st

             0                 1                 2                 3                 4

0    03BC6E8AEFBDFEF8  83F7A82D7A4464D3  405632D90FD95D97  C0908FBB7C8E2B8E  E1D631265FBD4093

1    8817133B2DBF06D6  3F2C4EAA71487AC9  8E4AD0A9A7FF20CA  8069268008F849E7  DC68089997AEAF8C

2    F1943021A11C88A9  17FF9E213690C782  4C979DBFB83DB5BE  7D2D4954D08040C1  C30E01160E3206BA

3    D0D28EBC822FE3B4  BC5D9A5BEE7F42EB  0C5D24309FCA6DBD  B6F2E61B805A36B4  E08301FAAB3E8FAC

4    8CFA479B83A566D0  24F5DDF87A7774E7  501433DEF17895AD  42AE9C1CDA6705F6  5CD59CB8469C7D84

5    07BD9F26C8310FB8  3D707C94DC84AD95  0C3CFAF9F0F210C9  9B75F7E0148DB580  F1C6FE5C9DA54FB7

6    EF039589B471619D  1E6AF037527B11D4  F4DA06DBBF4E6FB3  BF5498B9B7305A88  58B5B3DD0E28F1B0

7    40BA97D5864FCCD1  62F52BAAFC33BFAF  9E08D1AE595EE8F0  35D1FC9723D4C988  5F303B569645F4A1

8    D7A154B15E89AE86  405632D90FD95D97  C0908FBB7C8E2B8E  88E1D631265FBD40  03BC6E8AEFBDFEF8

The DSM-X channel hopping algorithm was found by Alexandr Alexandrov and Sergey Gimaev.

Channel hopping

DSM-X uses a 23-channel hopping sequence.  The sequence is based upon a unique Tx ID.

The channel hopping algorithm uses an LSR and is computed as follows.

id_tmp = ID = negate(CYRF MFGID + model #)

foreach idx in (0 .. 22):

  ok = 0

  while(ok is 0):

     id_tmp = id_tmp * 0x0019660D + 0x3C6EF35F   ## Randomization

     next_ch = ((id_tmp >> 8) MODULO 0x49) + 3      ## Use least-significant byte and must be larger than 3

     if (next_ch is odd and ID is odd OR next_ch is even and ID is even)

       AND none of the values in the 'ch' array are equal to next_ch:

         if 3 <= tmp < 28 and the number of channels in ch that are between 3 and 28 is < 8

           OR 28 <= tmp < 52 and the number of channels in ch that are between 28 and 52 is < 7

           OR 53 <= tmp and the number of channels in ch that are greater than 53 is < 8:

               ok = 1

  ch[idx] = next_ch

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