SP2-433-160 Datasheet, PDF (18/27 Pages) Radiometrix Ltd – UHF SpacePort Transceiver

Data
Each byte in the SP2's buffer is expanded into a 12 bit symbol prior to sending. The symbol coding has
the following properties :-
• Perfect 50:50 balance, i.e.. always 6 one's & 6 zero's
• There are never more than 4 consecutive one's or zero's. This minimises the low frequency
components in the code and allows fast settling times to be used for the receivers' data slicer.
• Minimum Hamming distance = 2, i.e.. each code is different from any other code by a minimum of 2
bits, thus all odd number of bit errors will always be detected.
• In general only 256 of 4096 (6.25%) possible codes are valid, i.e.. a 93.75 % probability of trapping a
byte error.
• Preamble and the Frame sync codes are not part of the symbol alphabet, a 'clash' signal will cause
immediate termination of the current decode followed by an attempt to lock to the new signal.
Check Sum
Since the receiver checks each symbol for integrity, a simple 8 bit check sum is used to test for overall
packet integrity. This is also coded into a 12 bit symbol prior to transmission.
Radiometrix Ltd, SP2 data sheet
page 18