FX919A Datasheet, PDF (12/44 Pages) CML Microcircuits – 4-Level FSK Modem Data Pump

4-Level FSK Modem Data Pump
FX919A
1.5.4 Frame Structure
Figure 7 below shows how an over-air message frame may be constructed from Frame and Symbol Sync
patterns, followed by one or more 'Header', 'Intermediate' or 'Last' blocks.
Byte 0
Byte 1
Byte 2
Byte 3
Byte 4
Byte 5
Byte 6
Byte 7
Byte 8
Byte 9
Byte 10
Byte 11
Header Block
76 5 432 1 0
Data Bytes
(10)
CRC1
(2 bytes)
Intermediate Blocks
7 6 5 43 2 1 0
Data Bytes
(12)
Last Block
7654 32 1 0
Data Bytes
(8)
CRC2
(4 bytes)
tri-bits
4-level
symbols
7
07
0
Byte 0
Byte 1
7
0
Byte 11
'000'
01 2 3 4 5
29 30 31 32
FEC TRELLIS CODING / DECODING
( ERROR CORRECTION )
01 2
64 65
INTERLEAVING / DE-INTERLEAVING
Over-air
signal
(symbols)
SYMBOL FRAME
SYNC
SYNC
24
FRAME
PREAMBLE
'HEADER'
BLOCK
66
INTERMEDIATE BLOCKS
66
66
FRAME
'LAST'
BLOCK
66
Frame Sync:
-1 +1 -1 +1 -1 +3 -3 +3 -3 -1 +1 -3 +3 +3 -1 +1 -3 -3 +1 +3 -1 -3 +1 +3
sent first
last
Symbol Sync : at least 24 symbols of '..+3 +3 -3 -3 ...' sequence
Figure 7 Over Air Signal Format
© 1996 Consumer Microcircuits Limited
12
D/919A/4