FX929A Datasheet, PDF (20/44 Pages) CML Microcircuits – 4-Level FSK Modem Data Pump

4-Level FSK Modem Data Pump
FX929A
TSID: Transmit Station ID
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'.
RESET: Stop any current action
This 'task' takes effect immediately, and terminates any current action (task, AQSC or AQLEV) 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
when VDD is applied, to set the modem into a known state.
Note that due to delays in the RRC filter, it will take several symbol times for any change to appear at the TXOP
pin.
Task Timings
Data to Data Block Buffer
Task to Command Register
IBEMPTY bit
BFREE bit
Symbols to
RRC filter
Modem Tx output
1
1
2
3
2
3
t4
t4
t4
t2
t1
t3
from task #1
t2
t3
from task #2
t2
t3
from task #3
Figure 10 Transmit Task Timing Diagram
t1 Modem in idle state. Time from writing first
task to application of first transmit bit to Tx
RRC filter
t2 Time from application of first symbol of the
task to the Tx RRC filter until BFREE goes
to a logic '1' (high).
t3 Time to transmit all symbols of the task
t4 Max time allowed from BFREE going to a
logic '1' (high) for next task (and data) to
be written to modem
Task
Any
T24S
TSID
THB/TIB/TLB
T4S
T24S/TSID
THB/TIB/TLB
T4S
T24S
TSID
THB/TIB/TLB
T4S
Time
(symbol times)
1 to 2
5
6
16
0
24
69
4
18
17
52
3
© 1996 Consumer Microcircuits Limited
20
D/929A/4