Chapter 10 - Voice Mode Operation
10-8
1. monitors the line we which connects the DCE to the remote station or to one
or more local devices t detect events which the DCE reports to the DTE.
These events pertain to signals carried over the line such as tones, and to
PSTN -generated control and notification signals such as ringing.
2. does not expect to receive digitized data from the DTE, perform conversion,
or transmit the analog signal to the remote station or to one or more local
devices.
The Voice Reception State is terminated by either of the following two methods:
1. The DCE receives <DLE><!> shielded code from the DTE.
2. The DCE receives characters other than <XON>, <XOFF> or a shielded
code from the DTE.
After termination of the Voice Data Reception State, the DCE enters the Voice
Command State.
Events and Actions with Shielded Code

Event Detection and Reporting

The voice mode may return many more event detection reports than the familiar
RING result code used in data/fax modems. While in voice mode, the DCE can
detect DTMF tones. The DCE will report the event to the DTE at the time of
detection by inserting a <DLE> shielded code into the data to the DTE. The form
of the report is <DLE><code>, where <code> can be one of the possible
character values listed in the following table.
<code> Event Report Description
<DLE> (0x10) Two contiguous <DLE><DLE> codes indicate a single <DLE> in
the data stream.
<SUB> (0x1A) <DLE><DLE> in the data stream.
<DC2> (0x12) Concatenate reception data streams. The DCE sends this code to
indicate the start of a new voice data stream with the same
parameters as the last stream for the purpose of a timing mark.
The DCE resets its compressors before transmitting the data after
the <DLE><DC2> codes. This resync generation timer is defined
by the command AT+VSY.
<ETX> (0x3) End Data State. The DCE sends this code to indicate the end of
the voice data.
R (0x52) Ring: The <DLE> shielded version of the RING result code
1 (0x31) DTMF 1
2 (0x32) DTMF 2
3 (0x33) DTMF 3
4 (0x34) DTMF 4
5 (0x35) DTMF 5
6 (0x36) DTMF 6