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.
Header Block
Intermediate Blocks
Last Block
7
6
5
4
3
2
1
0
7
6
5
4
3
2
1
0
7
6
5
4
3
2
1
0
Byte 0
Byte 1
Byte 2
Byte 3
Byte 4
Byte 5
Byte 6
Byte 7
Byte 8
Byte 9
Byte 10
Byte 11
Data Bytes
(10)
Data Bytes
(8)
Data Bytes
(12)
CRC2
(4 bytes)
CRC1
(2 bytes)
7
0
7
0
7
0
Byte 0
Byte 1
Byte 11
'000'
tri-bits
0
0
1
2
3
4
5
29
30
31
32
FEC TRELLIS CODING / DECODING
( ERROR CORRECTION )
4-level
symbols
1
2
64
65
INTERLEAVING / DE-INTERLEAVING
Over-air
signal
'HEADER'
BLOCK
SYMBOL
SYNC
FRAME
SYNC
'LAST'
BLOCK
INTERMEDIATE BLOCKS
(symbols)
24
66
66
66
66
FRAME
PREAMBLE
FRAME
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
ã 1996 Consumer Microcircuits Limited
12
D/919A/4
CMLMICRO [ CML MICROCIRCUITS ]
