BIM-433-40 Radiometrix, BIM-433-40 Datasheet - Page 12

Manufacturer Part Number

BIM-433-40

Description

Low Power UHF Data Transceiver Module

Manufacturer

Radiometrix

Datasheet

1.BIM-433-40.pdf (17 pages)

Radiometrix Ltd, BiM Data Sheet

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Method 3 - FEC coding

If only a subset of the ASCII code is required (e.g. 0-9 , A-Z and a few

control codes) then translate (via. a look up table) the required

ASCII codes into the 8 bit codes below. These codes all have a 50:50

mark/space when sent serially.

Of the 256 possible 8 bit codes, 70 contain 4 ones & 4 zeros. The 68 Hex codes below

have a 50:50 mark:space and may either be sent/received from a standard serial port

(UART) using 1 start, 1 stop and no parity or as bytes of a synchronous code. Use for this

subset also allows simple byte error checking on reception as all received codes must

contain exactly 4 one's and 4 zero's.

Other subsets are also possible e.g. a 10bit code has 1024 differs, 252 of which have 5

one's and 5 zero's i.e. a 50:50 M:S ratio.

Each byte is sent twice; true then it's logical compliment. e.g. even bytes are true and

odd bytes are inverted. this preserves a 50:50 balance.

A refinement of this simple balancing method is to increase the stagger between the true

and the inverted data streams and add parity to each byte. Thus the decoder may

determine the integrity of each even byte received and on a parity failure select the

subsequent inverted odd byte. The greater the stagger the higher the immunity to

isolated burst errors.

Bitrate , Max 40kbit/s , Min 2kbit/s

Redundancy (per byte) 25% (synchronous), 50% (async)

(note 0Fh & F0h have been omitted to minimise consecutive 0 or 1's)

Bit rate , Max 40kbit/s , Min 4.8kbit/s

Redundancy (per byte) 100%

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