Specifications

Chapter 17 – Audio Commands
Multi-Tech Systems, Inc. AT Commands for EDGE Modems (S000371B) 222
17.16 AT^SNFTTY Signal TTY/CTM Audio Mode
Capability
Description: The Multi-Tech wireless modem offers basic support for equipment using the CTM standard
(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.
Related documents: Refer to the relevant standards, such as 3GPP TS 26.226 (ETSI TS 126
226) and 3GPP TS 23.228 (ETSI TS 123 226). 3GPP documentation can be retrieved, for
example, from http://www.3gpp.org/specs/specs.htm. Application Note 22
“Using TTY/CTM
equipment” supplies information needed to connect TTY/CTM equipment to the Multi-Tech
wireless modem.
Requirements for using TTY/CTM features:
• TTY/CTM functionality requires audio mode 5 or 6 with all audio parameters set to their
factory default.
To do so, first enter the AT^SNFS command to select audio mode 5, 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.
• Depending on which audio interface the CTM device is connected to select the according
settings via AT^SAIC.
Test Command Syntax: AT^SNFTTY=?
Response: ^SNFTTY: (list of supported <audioState>s)
OK
Read Command Syntax: AT^SNFTTY?
Response: ^SNFTTY: <audioState>
OK
Write Command Syntax: AT^SNFTTY=<audioState>
Response: OK
ERROR
+CME ERROR: <err>
Parameter Description:
<audioState>
0 Audio path is in normal speech mode.
1 Audio path is in TTY/CTM mode.