CMX878 View Datasheet(PDF) - CML Microsystems Plc

Part Name

Description

Manufacturer

CMX878

Line Powered Modem plus DAA

CML Microsystems Plc 

Line Powered Modem plus DAA

CMX878

1. It is assumed that the CMX878 has powered up the regulator after detecting a ringing signal. The

microcontroller confirms this by reading the Line/Wakeup Event Register. It then powers up the xtal

and MODEM & TONES PROCESSOR circuits.

2. Connect the line (go off hook), set a 2150ms timer and power up the CMX878, setting the Tx Mode

Register to DTMF/Tones mode (set for ‘no tone’ at this time) and the Rx Mode Register to V.22

1200bps Low Band receive, descrambler enabled, Rx USART disabled.

3. When the 2150ms timer expires set the Tx Mode Register to transmit the 2100Hz answer tone and set

a 3300ms timer.

4. When the 3300ms timer expires set the Tx Mode Register to no tone and set a 75ms timer.

5. When the 75ms timer expires set the Tx Mode Register for V.22 High Band 1200bps transmission of

unscrambled 1s. Monitor the received signal for the S1 signal or scrambled 1s.

6. If scrambled 1s are detected for 270ms go to step 15.

7. If the S1 signal is received wait for it to end then set the Tx Mode Register for V.22 High Band

1200bps transmission of the S1 signal and set a 100ms timer.

8. When the 100ms timer expires set the Tx Mode Register for V.22 High Band 1200bps transmission of

scrambled 1s and set a 350ms timer.

9. When the 350ms timer expires set the Rx Mode Register for V.22bis Low Band 2400bps receive (this

will begin 16-way decisions) with the auto-equaliser and descrambler enabled and the Rx USART

disabled, set a 150ms timer and start to monitor for Rx scrambled 1s.

10. When the 150ms timer expires set the Tx Mode Register for V.22bis High Band 2400bps

transmission of scrambled 1s and set a 200ms timer.

11. Load the Tx Data Buffer with the first data to be transmitted.

12. Once 32 consecutive bits of received scrambled 1s at 2400bps have been detected, enable the Rx

USART.

13. 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.

14. A 2400bps data connection has now been established.

15. If scrambled 1s had been detected for 270ms in step 6, set the Tx Mode Register to V.22 High Band

1200bps scrambled 1s transmission and set a 765ms timer and enable the Rx USART.

16. Load the Tx Data Buffer with the first data to be transmitted.

17. When the 765ms 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 16.

18. A 1200bps data connection has now been established.

© 2002 Consumer Microcircuits Limited

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D/878/2

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