CMX969D5 MX-COM, Inc., CMX969D5 Datasheet - Page 10

• Manufacturer Part Number: CMX969D5
• Description: MOTIENT/ARDIS RD-LAP MDC4800 Modem
• Manufacturer: MX-COM, Inc.

MOTIENT
4.4 Frame Structure
In both RD-LAP and MDC modes the CMX969 performs all of the block formatting and de-formatting, the
binary data transferred between the modem and its µ C being that enclosed by the thick dashed rectangles
near the top of Figure 5 and Figure 6.
4.4.1
The CMX969 Frame Structure in MDC mode is illustrated in Figure 5, and consists of a Frame
Synchronization pattern followed by one or more 'Header’ blocks, one or more 'Intermediate’ blocks and a
'Last’ block. Channel Status bits are included at regular intervals. The first Frame of any transmission is
preceded by a Bit Synchronization pattern.
¤ ¤ ¤ ¤ 2001 MX-COM, Inc.
4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA
Over-air
signal
(bits)
SM
MDC Mode
/ARDIS
SM
SYNC
BIT
24
RD-LAP
FRAME
SYNC
40
Byte 0
Byte 1
Byte 2
Byte 3
Byte 4
Byte 5
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Channel
Status bits
TM
MDC4800 Modem
'HEADER'
BLOCK
112
7 6 5 4 3
Header Block(s)
Figure 5: MDC Over Air Signal Format
(4 bytes)
(2 bytes)
Byte 0
Address
Control
CRC1
ADDITIONAL
HEADER BLOCKS
&
112
INTERLEAVING / DE-INTERLEAVING
2 1 0
Byte 1
PACKET (1 TO 46 BLOCKS)
FEC CODING / DECODING
(ERROR CORRECTION)
Intermediate Blocks
7 6 5 4 3 2
FRAME
112 bits
10
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Data Bytes
(6)
INTERMEDIATE
BLOCKS
1 0
112
Byte 5
7 6 5 4 3 2 1 0
Data and Pad bytes
00000000
Last Block
(2 bytes)
CRC2
(4)
'LAST'
BLOCK
112
CMX969 Advance Information
FRAME
SYNC
NEXT FRAME
(OPTIONAL)
Doc. # 20480211.002