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CMX969P4

MOTIENT/ARDIS RD-LAP MDC4800 Modem

MX-COM Inc  

MOTIENTSM/ARDISSM RD-LAPTM MDC4800 Modem

10

CMX969 Advance Information

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 µC being that enclosed by the thick dashed rectangles

near the top of Figure 5 and Figure 6.

4.4.1 MDC Mode

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.

Byte 0

Byte 1

Byte 2

Byte 3

Byte 4

Byte 5

Header Block(s)

765 43 21 0

Address

&

Control

(4 bytes)

CRC1

(2 bytes)

Intermediate Blocks

7 65 43 21 0

Data Bytes

(6)

Last Block

7 654 321 0

Data and Pad bytes

(4)

CRC2

(2 bytes)

Byte 0 Byte 1

00000000

Byte 5

FEC CODING / DECODING

(ERROR CORRECTION)

Channel

Status bits

INTERLEAVING / DE-INTERLEAVING

112 bits

Over-air

signal

(bits)

BIT

SYNC

24

FRAME 'HEADER'

SYNC BLOCK

40

112

ADDITIONAL

HEADER BLOCKS

112

INTERMEDIATE

BLOCKS

112

'LAST'

BLOCK

112

FRAME

SYNC

PACKET (1 TO 46 BLOCKS)

FRAME

NEXT FRAME

(OPTIONAL)

Figure 5: MDC Over Air Signal Format

¤2001 MX-COM, Inc.

www.mxcom.com Tel: 800 638 5577 336 744 5050 Fax: 336 744 5054

Doc. # 20480211.002

4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA All trademarks and service marks are held by their respective companies.

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