Siemens Brodersen MC55 AT - Manual (Page 421)

MC55_ATC_V04.00 Page 421 of 475 3/17/06
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17.16 AT^SNFTTY Signal TTY/CTM audio mode capability
MC55 offers basic support for equipment using the CTM standard (Cellular Text Telephone Modems). The ben-
efit 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 MC55 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 MC55. 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 MC55.
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 eas-
ily be set with
AT^SNFD
.
• Depending on which audio interface the CTM device is connected to select the according settings via
AT^SAIC
.
Syntax
Parameter Description
0 Audio path is in normal speech mode.
1 Audio path is in TTY/CTM mode.
Test Command
AT^SNFTTY=?
Response(s)
^SNFTTY:
(list of supported
<audioState>
s)
OK
Read Command
AT^SNFTTY?
Response(s)
^SNFTTY: <audioState>
OK
Write Command
AT^SNFTTY= <audioState>
Response(s)
OK
ERROR
+CME ERROR: <err>
Reference(s) PIN ASC0 ASC1 MUX1 MUX2 MUX3 Charge  Last
SIEMENS % % % % % % ! ! !
<audioState>
(num)