MX919B View Datasheet(PDF) - CML Microsystems Plc
Part Name
Description
Manufacturer
MX919B Datasheet PDF : 48 Pages
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4-Level FSK Modem Data Pump
Page 19 of 47
MX919B PRELIMINARY INFORMATION
4.5.2.12 R4S: Read 4 Symbols
This task causes the modem to read the next 4 symbols and translate them directly (without de-interleaving or
FEC) to an 8-bit byte which is placed into the Data Block Buffer. The BFREE and IRQ bits of the Status
Register are then set to '1' to indicate that the µC may read the data byte from the Data Block Buffer and write
the next task to the Command Register.
This task is intended for special tests and channel monitoring - perhaps preceded by a SFS task.
Note: It is possible to construct message formats, which do not rely on the block formatting of the THB, TIB,
and TLB tasks. This can be accomplished by using T4S or T24S tasks to transmit and R4S to receive the
user's data. One should be aware, that the receive level and timing measurement circuits need to see a
reasonably 'random' distribution of all four possible symbols in the received signal to operate correctly.
Accordingly, binary data may benefit from scrambling before transmission if it is not reasonably 'random' to
start with.
4.5.2.13 T24S: Transmit 24 Symbols
This task, which is intended to facilitate the transmission of Symbol and Frame Sync patterns as well as
special test sequences, takes 6 bytes of data from the Data Block Buffer and transmits them as 24 4-level
symbols without any CRC or FEC.
Byte 0 of the Data Block Buffer is sent first, byte 5 last.
Once the modem has read the data bytes from the Data Block Buffer, the BFREE and IRQ bits of the Status
Register will be set to '1', indicating to the µC that it may write the data and command byte for the next task to
the modem.
The tables below show what data needs to be written to the Data Block Buffer to transmit the MX919B
Symbol and Frame Sync sequences:
‘Symbol Sync’
Symbols
+3 +3 -3 -3
+3 +3 -3 -3
+3 +3 -3 -3
+3 +3 -3 -3
+3 +3 -3 -3
+3 +3 -3 -3
Values written to Data Block Buffer
Binary
Hex
Byte 0: 11110101
F5
Byte 1: 11110101
F5
Byte 2: 11110101
F5
Byte 3: 11110101
F5
Byte 4: 11110101
F5
Byte 5: 11110101
F5
‘Frame Sync’
Symbols
-1 +1 -1 +1
-1 +3 -3 +3
-3 -1 +1 -3
+3 +3 -1 +1
-3 -3 +1 +3
-1 -3 +1 +3
Values written to Data Block Buffer
Binary
Hex
Byte 0: 00100010
22
Byte 1: 00110111
37
Byte 2: 01001001
49
Byte 3: 11110010
F2
Byte 4: 01011011
5B
Byte 5: 00011011
1B
4.5.2.14 THB: Transmit Header Block
This task takes 10 bytes of data (Address and Control) from the Data Block Buffer, calculates and appends
the 2-byte CRC1 checksum, translates the result to 4-level symbols (with FEC), interleaves the symbols, and
transmits the result as a formatted 'Header' Block.
Once the modem has read the data bytes from the Data Block Buffer, the BFREE and IRQ bits of the Status
Register will be set to '1'.
©2001 MX•COM, INC.
www.mxcom.com Tele: 800 638 5577 336 744 5050 Fax: 336 744 5054
Doc. # 20480170.003
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