FX929A Datasheet, PDF (12/44 Pages) CML Microcircuits – 4-Level FSK Modem Data Pump

4-Level FSK Modem Data Pump
FX929A
1.5.4 Frame Structure
The FX929A 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.
Byte 0
Byte 1
Byte 2
Byte 3
Station ID
msb
lsb
765 43 21 0
System ID
Domain ID
Base ID
CRC0
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
7 65 4 3 21 0
Address
&
Control
(10 bytes)
CRC1
(2 bytes)
Intermediate Blocks
7654321 0
Data Bytes
(12)
Last Block
76 543 21 0
Data bytes
(0 - 8)
Pad bytes
(0 - 8)
CRC2
(4 bytes)
7
07
07
07
20
Byte 0
Byte 1
Byte 2
Byte 3
'000'
012
8 9 10
tri-bits
7
07
0
Byte 0
Byte 1
012345
7
0
Byte 11
'000'
29 30 31 32
FEC TRELLIS CODING / DECODING
( ERROR CORRECTION )
01
20 21
4 -lev el
sy m bols
FEC TRELLIS CODING / DECODING
( ERROR CORRECTION )
012
INTERLEAVING / DE-INTERLEAVING
64 65
Block:
22 symbols
S
22 symbols
S
22 symbols
S
Over-air
signal
(symbols)
SYMBOL
SYNC
24
FRAME
SYNC
S
STATION
ID
'HEADER'
S _BLOCK
24 1 22
1
69
FRAME
PREAMBLE
INTERMEDIATE BLOCKS
69
69
PACKET (1 TO 44 BLOCKS)
FRAME
'LAST'
BLOCK
69
FRAME
SYNC
NEXT FRAME
(OPTIONAL)
'S' : Channel Status Symbol : +3 = Busy +1 = Unknown -1 = Unknown -3 = Idle
Frame Sync:
-1 +1 -1 +1 -1 +3
Symbol Sync:
+3 +3 -3 -3 +3 +3
sent first
-3 +3 -3 -1 +1 -3 +3 +3
-3 -3 +3 +3 -3 -3 +3 +3
-1 +1 -3 -3 +1 +3 -1
-3 -3 +3 +3 -3 -3 -3
-3 +1 +3
-3 +3 +3
last
Figure 7 Over Air Signal Format
© 1996 Consumer Microcircuits Limited
12
D/929A/4