4-Level FSK Modem Data Pump
FX929B
1.5.4
Frame Structure
The FX929B Frame Structure as used in a RD-LAP system is illustrated in Figure 7, and consists of a Frame
Preamble (comprising a 24-symbol Frame Synchronisation pattern and Station ID block) followed by a 'Header
Block', one or more 'Intermediate Blocks and a 'Last Block'. Channel Status (S) symbols are included at
regular intervals. The first Frame of any transmission is preceded by a Symbol Synchronisation pattern.
Header Block
Intermediate Blocks
Last Block
Station ID
msb
7
lsb
0
6
5
4
3
2
1
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
System ID
Domain ID
Byte 0
Byte 1
Byte 2
Byte 3
Byte 4
Byte 5
Byte 6
Byte 7
Byte 8
Data bytes
(0 - 8)
Byte 2
Byte 3
Base ID
CRC0
Address
&
Data Bytes
(12)
Control
Pad bytes
(0 - 8)
(10 bytes)
CRC2
(4 bytes)
Byte 9
Byte 10
CRC1
(2 bytes)
Byte 11
2
7
0
2
7
0
7
0
7
0
7
0
2
7
0
7
0
Byte 0
Byte 1
Byte 2
Byte 3
Byte 0
Byte 1
Byte 11
'000'
'000'
10
0
1
9
8
tri-bits
0
0
1
1
3
4
5
29
30
31
32
FEC TRELLIS CODING / DECODING
( ERROR CORRECTION )
FEC TRELLIS CODING / DECODING
( ERROR CORRECTION )
4 -level
65
2
64
0
1
21
20
sy m bols
INTERLEAVING / DE-INTERLEAVING
Block:
S
S
22 symbols
S
22 symbols
22 symbols
Over-air
signal
'HEADER'
BLOCK
SYMBOL
SYNC
FRAME
SYNC
STATION
ID
FRAME
SYNC
'LAST'
BLOCK
S
S
INTERMEDIATE BLOCKS
(symbols)
1
24
24
1
22
69
69
69
69
PACKET (1 TO 44 BLOCKS)
FRAME
FRAME
PREAMBLE
NEXT FRAME
(OPTIONAL)
'S' : Channel Status Symbol : +3 = Busy +1 = Unknown -1 = Unknown -3 = Idle
Frame Sync:
-1
+1
-1
+1
-1
+3
-3 +3
-3
-1 +1
-3 +3
+3
+3
-1
-3
+1
-3
-3 +1
+3
-3
-1
-3
-3 +1
-3 +3
+3
Symbol Sync:
+3 +3
-3
-3 +3
+3
-3
-3 +3
+3
-3
-3 +3
-3 +3
+3
-3
+3
sent first
last
Figure 7 Over Air Signal Format
ã 1997 Consumer Microcircuits Limited
12
D/929B/1
CMLMICRO [ CML MICROCIRCUITS ]
