DB929B Datasheet, PDF (21/51 Pages) CML Microcircuits – Full Data Packet Framing

4-Level FSK Modem Data Pump
Page 21 of 50
MX929B PRELIMINARY INFORMATION
4.5.2.14 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, FEC, interleaving, or adding any 'S' symbols.
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 MX929B 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:
01011111
5F
'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
4.5.2.15 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, inserting 'S' symbols at 22 symbol intervals.
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'.
4.5.2.16 TIB: Transmit Intermediate Block
This task takes 12 bytes of data from the Data Block Buffer, updates the 4-byte CRC2 checksum for inclusion
in the 'Last' block, translates the 12 data bytes to 4-level symbols (with FEC), interleaves the symbols, and
transmits the result as a formatted 'Intermediate' Block, inserting 'S' symbols at 22-symbol intervals.
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'.
4.5.2.17 TLB: Transmit Last Block
This task takes 8 bytes of data from the Data Block Buffer, updates and appends the 4-byte CRC2 checksum,
translates the resulting 12 bytes to 4-level symbols (with FEC), interleaves the symbols, and transmits the
result as a formatted 'Last' Block, inserting 'S' symbols at 22-symbol intervals.
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'.
4.5.2.18 T4S: Transmit 4 Symbols
This task is similar to T24S but takes only one byte from the Data Block Buffer, transmitting it as four 4-level
symbols.
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