CMX878D6 View Datasheet(PDF) - CML Microsystems Plc
Part Name
Description
MFG CO.
'CMX878D6' PDF : 63 Pages View PDF
Line Powered Modem plus DAA
CMX878
3. On detection of the 2100Hz answer tone wait for it to end then wait for the 2225Hz answer tone
detector to respond. (The ‘2225Hz’ answer tone detector will recognise unscrambled binary 1s at
1200bps High Band as well as 2225Hz). When unscrambled binary 1s or 2225Hz have been received
for 155ms set a 456ms timer.
4. When the 456ms timer expires check that the 2225Hz or unscrambled 1s is still being received, then
set the Tx Mode Register for V.22 1200bps Low Band transmission of S1 signal and set a 100ms
timer. Also set the Rx Mode register to V.22 1200bps High Band receive, descrambler enabled and
Rx USART disabled.
5. When the 100ms timer expires set the Tx Mode Register for V.22 1200bps Low Band transmission of
scrambled 1s (continuous 1s with the scrambler enabled) and look for received S1 signal.
6. If the S1 signal is not detected within 270ms then go to step 14 as the answering modem is not
capable of 2400bps operation.
7. If S1 signal is detected wait for it to end then set a 450ms timer.
8. When the 450ms timer expires set the Rx Mode Register to V.22bis 2400bps High Band (this will
begin 16-way decisions) with the auto-equaliser and descrambler enabled. Start to monitor for Rx
scrambled 1s. Set a 150ms timer.
9. Once 32 consecutive bits of received scrambled 1s at 2400bps have been detected, enable the Rx
USART.
10. When the 150ms timer expires set the Tx Mode Register for V.22bis 2400bps scrambled 1s, set a
200ms timer.
11. Load the Tx Data Register with the first data to be transmitted.
12. When the 200ms timer expires set the Tx Mode Register for Start-Stop or Synchronous transmission
of data from the Tx Data Buffer. This will start transmission of the data loaded in step 11.
13. A 2400bps data connection has now been established.
14. If the S1 signal had not been detected within 270ms after step 5 then monitor for scrambled 1s at
1200bps.
15. When scrambled 1s (at 1200bps) have been received for 270ms enable the Rx USART, set a 765ms
timer and load the Tx Data Register with the first data to be transmitted.
16. When the timer expires set the Tx Mode Register for Start-Stop or Synchronous transmission of data
from the Tx Data Buffer. This will start transmission of the data loaded in step 15.
17. A 1200bps data connection has now been established.
1.6.4 V.22bis Answering Modem Application
This section describes how the CMX878 can be used in a V.22bis Answering modem application,
employing V.25 automatic answering and the V.22bis recommended handshake sequence. A 1200 or
2400 bps connection will be established depending on the signals received from the calling modem.
© 2002 Consumer Microcircuits Limited
50
D/878/2
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