EV6240 datasheet(39/47 Pages) CMLMICRO

39 / 47 page

Evaluation Kit for CMX624/CMX644A

EV6240

UM6240/3

1.6.6.5 V22/Bell 212A Handshaking Sequence for an EV6240 Calling Modem via a 2-Wire Line

Figure 10 is a flowchart illustrating the firmware handshaking sequence performed when an on-board

CMX644A modem originates a call to an external V22/Bell 212A simulator/modem.

The firmware assumes the external equipment has been configured to answer the call using the

appropriate protocol.

The states shown in the diagram are as follows:

Calling Modem Entry Point

On entry the Modem will be off-hook, DTMF dialling and the required call progress monitoring

completed.

State 1

Start the Wait for Carrier after Dial Timer (setting stored in S7).

Check Communications Standard selected by user (Bell or ITU-T).

If Bell

Set up CMX644A to detect 2225Hz Answer tone.

Goto State 6.

State 2

Set up CMX644A to detect 2100Hz Answer tone.

Start transmitting the 1300Hz Calling tone (Cadence 0.6s on and 1.5s off).

State 3

If the 2100Hz Answer tone is detected then start Validation Timer (setting stored in S18).

If the 2100Hz Answer tone is detected for 1s stop transmitting the 1300Hz Calling Tone then goto

State 4.

If the Wait for Carrier after Dial Timer expires then Hang Up and Exit.

State 4

Wait until silence occurs (2100Hz Answer tone not detected)

Start a 60ms Timer.

Set up CMX644A to detect 2225Hz Answer tone (set up will allow for frequency detection of

either the 2225Hz Answer tone or High Band Unscrambled PSK 1’s (marks))

Goto State 5.

If Validation Timer expires the 2100Hz Answer tone has been present for too long so Hang Up and

Exit.

EV6240 Datasheet(PDF) 39 Page - CML Microcircuits