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CMX969P4

MOTIENT/ARDIS RD-LAP MDC4800 Modem

MX-COM Inc  

MOTIENTSM/ARDISSM RD-LAPTM MDC4800 Modem

18

CMX969 Advance Information

4.6.1.5 TIB: Transmit Intermediate Block (RD-LAP and MDC)

In RD-LAP mode 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.

In MDC mode this task takes 6 bytes of data from the Data Block Buffer, updates the 2-byte CRC checksum

for inclusion in the 'Last' block, adds FEC bits, interleaves the result, inserts channel status bits and transmits

the result as a formatted ‘Intermediate’ 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'.

4.6.1.6 TLB: Transmit Last Block (RD-LAP and MDC)

In RD-LAP mode 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.

In MDC mode this task takes 4 bytes of data from the Data Block Buffer, updates and appends the 2-byte

checksum, adds FEC bits, interleaves the result, inserts channel status bits and transmits the result as a

formatted ‘Last’ 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'.

4.6.1.7 T4S: Transmit 4 Symbols (RD-LAP only)

This task is similar to T24S but takes only one byte from the Data Block Buffer, transmitting it as four 4-level

symbols most significant bit first.

4.6.1.8 T8B: Transmit 8 Bits (MDC only)

This task is similar to T40B but takes only one byte from the Data Block Buffer, transmitting it as 8 bits.

4.6.1.9 TSID: Transmit Station ID (RD-LAP only)

This task takes 3 ID bytes from the Data Block Buffer, calculates and appends the 6-bit CRC0 checksum,

translates the result to 4-level symbols (with FEC) and transmits the resulting 22 symbols preceded and

followed by 'S' symbols.

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'.

4.6.1.10 RESET: Stop any current action

This 'task' takes effect immediately, and terminates any current task the modem may be performing and sets

the BFREE bit of the Status Register to '1', without setting the IRQ bit. It should be used (after a delay to allow

the Xtal oscillator to start up) when VDD is applied or the ZP bit of the Mode Register changed from ‘1’ to ‘0’ to

set the modem into a known state.

Note that due to delays in the transmit low pass filter, it will take several symbol times for any change to

appear at the TXOUT pin.

¤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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