DB929B datasheet(14/51 Pages) CMLMICRO

14 / 51 page

4-Level FSK Modem Data Pump

Page 14 of 50

MX929B PRELIMINARY INFORMATION

www.mxcom.com Tel: 800 638 5577 336 744 5050

Fax: 336 744 5054

Doc. # 20480171.003

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All trademarks and service marks are held by their respective companies.

4.3

Binary to Symbol Translation

Although the over-air signal, and therefore the signals at the modem TXOUT and RXIN pins, consists of 4-

level symbols, the raw data passing between the modem and the µC is in binary form. Translation between

binary data and the 4-level symbols is done in one of two ways, depending on the task being performed.

1. Direct way: (simplest form) - converts between two binary bits and a single symbol, such as the 'S'

Channel Status symbol.

SYMBOL

MSB

LSB

-1

-3

Accordingly, 1 byte = 4 symbols = 8 bits, and one byte translates to four symbols for the T4S and R4S tasks

and six bytes translates to twenty-four symbols for the T24S task described in Section 4.5.2.

MSB

LSB

Bits:

Symbols:

send first

send last

2. FEC way: (more complicated) - essentially translates groups of 3 binary bits to pairs of 4-level symbols

using a Forward Error Correcting coding scheme for the block oriented tasks THB, TIB, TLB, RHB, RILB,

and RSID described in Section 4.5.2.

DB929B Datasheet(PDF) 14 Page - CML Microcircuits