EV6240 Datasheet, PDF (37/47 Pages) CML Microcircuits – Opto-Isolated serial interface capability

Evaluation Kit for CMX624/CMX644A
EV6240
1.6.6.4 V23/Bell 202 Handshaking Sequence for an EV6240 Answering Modem via a 2-Wire Line
Figure 9 is a flowchart illustrating the firmware handshaking sequence performed when an on-board
CMX624 modem answers a call from an external V23/Bell 202 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 10
Wait for Billing Delay Timer to expire.
Check Communications Standard selected by user (Bell or ITU-T).
If Bell goto State 14.
State 11
Set up CMX624 to Tx 2100Hz Answer tone.
Start 3.3 second Answer Tone Timer.
State 12
Wait for Answer Tone Timer to expire.
Turn off Tone o/p (silence).
Start 80ms Silence Timer.
State 13
Wait for Silence Timer to expire.
State 14
Set up the CMX624 to Tx High Band FSK 1’s (marks)
State 15
Set up CMX624 to detect Low Band FSK.
Start Validation Timer (setting stored in S18).
When the Rx Energy flag is set the Rx data is monitored to ensure 95% of 1’s are detected for 160ms.
If 95% of Low Band FSK 1’s are detected for 160ms
Turn on Modem CD LED.
Goto Data Transfer Mode.
If Validation Timer expires before 95% of Low Band FSK 1’s detected then Hang Up and Exit.
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UM6240/3