EV6240 Datasheet, PDF (42/47 Pages) CML Microcircuits – Opto-Isolated serial interface capability

Evaluation Kit for CMX624/CMX644A
EV6240
1.6.6.6 V22/Bell 212A Handshaking Sequence for an EV6240 Answering Modem via a 2-Wire Line
Figure 11 is a flowchart illustrating the firmware handshaking sequence performed when an on-board
CMX644A modem answers a call from an external V22/Bell 212A simulator/modem.
The firmware assumes the external equipment has been configured to originate the call using the
appropriate protocol.
The states shown in the diagram are as follows:
Answering Modem Entry Point
On entry the Modem will have manually answered a call using the ATA command or auto-answered
via the ring detect circuitry. In both cases the Modem will be off-hook.
Start 2 second Billing Delay Timer
State 11
Wait for Billing Delay Timer to expire.
Check Communications Standard selected by user (Bell or ITU-T).
If Bell goto State 15.
State 12
Set up CMX644A to Tx 2100Hz Answer tone.
Start 3.3 second Answer Tone Timer.
State 13
Wait for Answer Tone Timer to expire.
Turn off Tone o/p (silence).
Start 80ms Silence Timer.
State 14
Wait for Silence Timer to expire.
Set up the CMX644A to Tx High Band Unscrambled PSK 1’s (marks) with Guard Tone if selected.
State 15
Set up CMX644A to Tx 2225Hz Answer tone.
State 16
Set up CMX644A to detect Low Band Scrambled PSK.
Start Validation Timer (setting stored in S18).
When the PSK Carrier Detect flag is set the Rx data is monitored to ensure 95% of 1’s are detected
for 270ms.
If 95% of Low Band Scrambled PSK 1’s are detected for 270ms then goto State 17.
If Validation Timer expires before 95% of Low Band Scrambled PSK 1’s detected then Hang Up and
Exit.
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© 1999 Consumer Microcircuits Limited
UM6240/3