MilesTag Data Protocol

MilesTag II Data Protocol (V5.3X, MicroMT)

    In the MilesTag system, each time a "shot" is fired, the gun (transmitter) sends a short burst of data encoded onto an infrared carrier signal to the target sensor (receiver).  The data transmitted is composed of 16 bits in the form of a 2-byte data packet, and is essentially the equivalent of an infrared "bullet".  No laser is used in this system, but rather a high-powered infrared LED focused through a lens.  When the receiver is "hit" by the infrared signal, it will attempt to decode the data packet.  If a valid data packet is decoded by the receiver, the receiver will determine whether it is a weapon hit or system message and respond accordingly.  If the packet is incomplete, contains errors, or cannot be correctly decoded, the signal is counted as a "near-miss".

  Infrared Carrier Signal

    At this time, the carrier frequency is selectable between 38KHz/40KHz/56KHz.  This carrier frequency range was selected primarily for the availability of low cost demodulator ICs (Vishay, Panasonic, etc.).  These devices greatly simplify the design of the receiver circuit.  Also these frequencies are easily generated by a PIC processor operating on the 4MHz or 8MHz internal oscillator.  Matching infrared LEDs (940nm wavelength) are also widely available at low cost.

The system's transmit carrier frequency must be matched to the sensor used.

  Data Packet

    The MilesTag data packet consists of a header pulse followed by 16 data bits (two 8-bit data bytes) and 1 parity bit.  The header pulse and data bits are encoded onto a 40KHz infrared carrier signal using pulse-length modulation.  This modulation is identical to the format used in Sony IR remotes and others.

  Parity Bit (also serves as GameID bit)

    The Parity Bit is the Last Bit Transmitted (17th bit), and performs two functions.  First, for increased error detection capability, the parity bit can detect single-bit errors in the data packet.  The receiver will then reject any packets with incorrect parity.   (This protection is additional to the bit-by-bit error checking implemented by the receiver code).  Second, the user may select between Even or Odd parity by changing the GameID.  GameA uses Even Parity; and GameB uses Odd Parity.  This allows two separate games to be conducted using the MilesTag system without interference from one another (hits from the other game will only cause a "near miss" indication, but no hits can be scored between games).

    How the Parity Bit works (Even Parity):  As the 16-bit data packet is transmitted, the "1"s in the data packet are counted.  If the total number of "1"s is Even, then a "0" is transmitted as the 17th bit.  If the total number of "1"s is Odd, then a "1" is transmitted as the 17th bit.  So, for Even Parity, the transmitter ensures that the data packet always contains an even number of "1"s.  The receiver can then simply count all the "1"s in the incoming data packet including the parity (17th) bit.  If the total number of "1"s is Even, then the received data is assumed to be good.

    **See parity examples at bottom of this page.

  Pulse-Length Modulation

    In this modulation scheme, the value of the data bits ("1" or "0") and the header pulse are represented by the length of the pulse.  Each pulse is a burst of 40 KHz infrared light lasting the period (length) of the corresponding data bit.

• The Header Pulse is represented by a pulse (40 KHz carrier ON) with a period of 2400 uS (microseconds).

• A bit value of "1" is represented by a pulse (40 KHz carrier ON) with a period of 1200 uS. 

• A bit value of "0" is represented by a pulse (40 KHz carrier ON) with a period of 600 uS. 

• The space (40 KHz carrier OFF) between each of the bit pulses is 600uS.

Thus, a complete data packet will have a maximum length (all "1"s) of  33.0 milliseconds, and a minimum length (all "0"s) of  22.8 milliseconds.

 

To put this in terms of the max firing rate for a weapon, you can achieve rates of 29 rounds per second or 1785 rounds per minute.

  Data Bytes

    The data bytes are transmitted MSB first.  The first byte transmitted is Databyte1 and the second byte is Databyte2.

 

Databyte1 (Team & Player ID):

  MSB

TeamID (t)

TeamID (t)

TeamID (t)

PlayerD (p)

PlayerID (p)

PlayerID (p)

PlayerID (p)

PlayerID (p)

 

TeamID   ppppp = PlayerID

001ppppp  Team1 (Red)    

010ppppp  Team2 (Blu)

011ppppp  Team3 (Yel)

100ppppp  Team4 (Grn)

101ppppp  Team5 (Blk)

110ppppp  Team6 (Wht)

111ppppp  Team7 (Pur)

000mmmmm  System Message 

PlayerID   ttt = TeamID

ttt00000  Player0       

ttt00001  Player1

ttt00010  Player2

ttt00011  Player3

ttt00100  Player4

Etc…

ttt11111  Player31

System Messages                                               

00000000  Undefined

00000001  Add Health         

00000010  Add Rounds         

00000011  Add Clips          

00000100  Add RPG Rounds     

00000101  Non-player Hit     {wwwddddd}

00000110  Disable Weapon     

00000111  Secure Code A      

00001000  Secure Code B      

00001001  God Gun Functions  

00001010  Collateral Damage  

00001011  Game Select        

00001100  Weapon Select

00001101  Undefined

00001110  Undefined

00001111  Sys Ex Data

00010000  Score Data Header

00010001  Score Request

00010010  Undefined

00010011  Undefined

00010100  Undefined

00010101  Undefined

00010110  Set Team ID

00010111  Set Player ID

00011000  Undefined

00011001  Undefined

00011010  Undefined

00011011  Undefined

00011100  Undefined

00011101  Undefined

00011110  Undefined

00011111  Undefined

Non-Player Hit   www = WeaponID     ddddd = damage value (multiply by 2)

000ddddd  Claymore (Clmr)

001ddddd  Grenade (Grnd)

010ddddd  50 cal Machine Gun (tripod mounted) (50ca)

011ddddd  Rocket (Rckt)

100ddddd  Mortar (Mrtr)

101ddddd  Sentry (sensor operated gun) (Snty)    

110ddddd  Chemical (Chem)

111ddddd  Radiation (Nuke)

 

Databyte2  (Hit Points / Control Function):

  MSB

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

 

(See Table-B , Table-C , Table-D)

 

 

Clone Data Transfer: (MilesTag)    [0Fh]--[00h]--[FFh]--[Parameter1]--[Parameter2].......[ParameterXX]--[Checksum]

• The number, order and type of cloned parameters are specific to a particular device or system (MilesTag, FragTag, etc) so they are not defined here. This allows designers to customize the features of their systems while still maintaining compatibility with other MilesTag-based systems.

  DATA EXAMPLES  

This should help demonstrate how simple it is to construct MilesTag packets.  All examples show Even Parity (GameA).

Typical shot fired from player's weapon:  (anti-personnel ammo)

0100 0011 0000 1100 1

Team 2; Player 3; 12 hit points (3 hit points against base); parity

Typical shot fired from player's weapon:  (anti-base ammo)

1111 0100 1000 0010 1

Team 7; Player 20; 30 hit points against base; parity

Resurrect Opponent command fired from player's weapon:

1010 1000 0000 0000 1

Team 5; Player 8; Resurrect opponent; parity

Configure Receiver command transmitted from God Gun:

0000 1001 0000 1001 0

System message; God Gun; Configure Gun; parity

Load 6 clips into gun from "ammo box":

0000 0011 0000 0110 0

System message; Load Clips; 6; parity

Shot fired from 50 cal tripod mounted weapon:

0000 0101 0100 1101 0

System message; Non-player Weapon; 50 cal; 26 hit points; parity