At^snftty Signal Tty/Ctm Audio Mode Capability - Multi-Tech MultiModem EDGE Reference Manual

16.16 AT^SNFTTY Signal TTY/CTM Audio Mode Capability

The Multi-Tech wireless modem offers basic support for equipment using the CTM standard
Description:
(Cellular Text Telephone Modems). The benefit of CTM is that text characters typed on a TTY
device (Text Telephone Type-writer) can be transformed into special audio burst signals for
reliable transmission via the existing speech channels of a cellular phone system.
If CTM mode is activated, the ME will set the necessary bearer capability bit on outgoing (mobile
originated) calls and incoming calls with this bearer capability bit set are accepted. The TE needs
to decode the special audio burst signals.
If CTM mode is disabled, the ME will clear the bearer capability bit on mobile originated calls and
incoming calls with the bearer capability bit set are rejected because the Multi-Tech wireless
modem expects that CTM coded speech data cannot be decoded by the TE.
Designed to set the module's speech system into CTM mode, the AT^SNFTTY command allows
a CTM device to be connected to one of the three audio interfaces of the Multi-Tech wireless
modem. Traditional TTY devices that do not incorporate CTM functionality can be connected
through an external TTY-to-CTM adapter.
Requirements for using TTY/CTM features:
•
•
Test Command Syntax:
Response:
Read Command Syntax:
Response:
Write Command Syntax:
Response:
Parameter Description:
<audioState>
This parameter is non-volatile.
0
1
Multi-Tech Systems, Inc. AT Commands for EDGE Modems (S000371G)
TTY/CTM functionality requires audio mode 5 or 6 with all audio parameters set to their
factory default.
To activate TTY/CTM mode, first enter the AT^SNFS command to select audio mode 5 or
6, then use AT^SNFI and AT^SNFO to restore the default values. Alternatively, factory
defaults of all audio parameters in audio modes 2 - 6 can easily be set with AT^SNFD. To
deactivate TTY/CTM mode make sure that either audio mode 5 or 6 is set. Keep in mind
that the TTY/CTM mode is non-volatile. The audio mode, however, is volatile (power-up
default is audio mode 1) unless stored to the user defined profile with AT^SNFW.
Therefore, if restarted while in TTY/CTM mode the ME may need to be reconfigured for
audio mode 5 or 6 before the TTY/CTM mode is selectable again after the reboot.
Depending on which audio interface the CTM device is connected to select the according
settings via AT^SAIC.
AT^SNFTTY=?
^SNFTTY: (list of supported <audioState>s)
OK
AT^SNFTTY?
^SNFTTY: <audioState>
OK
AT^SNFTTY=<audioState>
OK
ERROR
+CME ERROR: <err>
Audio path is in normal speech mode.
Audio path is in TTY/CTM mode.
Chapter 16 – Audio Commands
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