CMX969D5 MX-COM, Inc., CMX969D5 Datasheet - Page 16

• Manufacturer Part Number: CMX969D5
• Description: MOTIENT/ARDIS RD-LAP MDC4800 Modem
• Manufacturer: MX-COM, Inc.

MOTIENT
4.6 CMX969 Modem Tasks
4.6.1
When the modem is in transmit mode, all tasks other than NULL or RESET instruct the modem to transmit
data from the Data Buffer, formatting it as required. The µC should therefore wait until the BFREE (Buffer
Free) bit of the Status Register is '1', before writing the data to the Data Block Buffer, then it should write the
desired task to the Command Register. If more than 1 byte needs to be written to the Data Block Buffer, byte
number 0 of the block should be written first.
Once the byte containing the desired task has been written to the Command Register, the modem will:
This lets the µC write a task and the associated data to the modem while the modem is still transmitting the
data from the previous task.
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4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA
B2
SM
Transmit Mode
Set the BFREE (Buffer Free) bit of the Status Register to '0'.
Take the data from the Data Block Buffer as quickly as it can - transferring it to the Interleave Buffer
for eventual transmission. This operation will start immediately if the modem is 'idle' (i.e. not
transmitting data from a previous task), otherwise it will be delayed until there is sufficient room in the
Interleave Buffer.
Once all of the data has been transferred from the Data Block Buffer, the modem will set the BFREE
and IRQ bits of the Status Register to '1' (causing the chip IRQ output to go low if the
the Mode Register has been set to '1'). This tells the µC that it may write new data and the next task
to the modem.
0
0
0
0
1
1
1
1
/ARDIS
B1
Task from µC to Command Register
IRQ bit of Status Register
IRQ output (
Data from µC to Block Buffer
BFREE bit of Status Register
TXOUT signal
1
0
0
1
1
0
0
1
SM
RD-LAP
B0
0
1
0
1
0
1
0
1
IRQ
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NULL
T24S
THB
TIB
TLB
T4S
TSID
RESET
TM
EN = '1')
MDC4800 Modem
Transmit 24 symbols
Transmit Header Block
Transmit Intermediate Block
Transmit Last Block
Transmit 4 symbols
Transmit Station ID
Cancel any current action
Figure 9: Transmit Task Overlapping
RD-LAP
Task 1
16
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from task 1
NULL
T40B
THB
TIB
TLB
T8B
RESET
-
Transmit 40 bits
Transmit Header Block
Transmit Intermediate Block
Transmit Last Block
Transmit 8 bits
Unused
Cancel any current action
Task 2
MDC
CMX969 Advance Information
from task 2
Doc. # 20480211.002
IRQ
EN
bit of