MX909A 데이터 시트보기 (PDF) - MX-COM Inc
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MX909A Datasheet PDF : 38 Pages
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GMSK Modem Data Pump
Page 10 of 37
MX909A PRELIMINARY INFORMATION
Mobitex¥ Frame Structure cont...
2 bytes of frame sync:
System specific.
2 bytes of control data.
1 byte of FEC code, 4 bits for each of the control bytes:
bits 7-4 (leftmost) operate on the first control byte.
bits 3-0 (rightmost) operate on the second control byte.
Each byte in the Frame Head is transmitted bit 7 (MSB) first to bit 0 (LSB) last.
The Data Block consists of:
18 bytes of data.
2 bytes of CRC calculated from the 18 data bytes.
4 bits of FEC code for each of the data and CRC bytes
The resulting 240 bits are interleaved and scrambled before transmission.
The over air signal is composed of Frame Sync and Bit Sync patterns, Control bytes, and Data Blocks as
shown in Figure 6.
The binary data transferred between the modem and the host µC is shown in the Frame Head and Data Block
of Figure 6 as shaded areas.
Frame Head
MSB
LSB
Byte 7 6 5 4 3 2 1 0
loaded first 0
Bit Sync 1
1
Bit Sync 2
2
Frame Sync 1
3
Frame Sync 2
4
Control Byte 1
loaded last 5
Control Byte 2
6
FEC1
FEC2
Data Block
MSB
LSB
Byte 7 6 5 4 3 2 1 0 3 2 1 0
loaded first 0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
loaded last 17
18
19
Data
(18 bytes)
CRC (2 bytes)
FEC
INTERLEAVING / DE-INTERLEAVING
SCRAMBLE / DESCRAMBLE
OVER - AIR
SIGNAL
BITS
BIT
SYNC
16
FRAME
SYNC
CTRL
BYTES
16
16
FRAME HEAD
FEC
8
DB 0 DB 1 DB 2 DB 3 DB 4
DATA
BLOCKS
DATA BLOCKS (0 to 32)
DB n
FRAME
Figure 6: Mobitex¥ Over Air Signal Format
¤2001 MX-COM, Inc.
www.mxcom.com Tel: 800 638 5577 336 744 5050 Fax: 336 744 5054
Doc. # 20480134.005
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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