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Chapter 6 – Voice Commands
SocketModem Global MT5634SMI Developer’s Guide 51
Command: +VGT=<level> Set the Volume for Transmitted Voice Samples
Result Codes: OK if the modem accepts the command; ERROR if the parameter is out of range.
Description: The +VGT= command causes the modem to set the volume control, either by attenuating or
amplifying the signal, for the transmitted voice samples. Values larger than 128 indicate a larger
gain than nominal, and values smaller than 128 indicate a gain smaller than nominal. The modem
may limit the receive gain to a narrower range, such as from 120 to 136, or from 120 to 128. The
value 0 is reserved for modem automatic volume control (AVC).
Warning: The modem will limit the transmit level over the Telco lines, regardless of the current
+VGT setting, to that permitted by CFR FCC Rules Part 68 – Subpart D.
Command: +VIT=<timer> Set DTE/DCE Inactivity Timer
Result Codes: OK if the modem accepts the command; ERROR if the parameter is out of range.
Description: The +VIT command sets the modem's initial value for the PC/Modem Inactivity Timer. The
permitted range is displayed by the +VIT=? command. The units are in 1.0 seconds. The PC can
disable the Inactivity Timer by using a value of 0 (+VIT=0).
The Inactivity Timer serves to ensure that the PC does not leave the modem in a state where it is
not accessible by voice-unaware software. The Inactivity Timer is activated when the PC selects
the voice fixed-rate. The timer expires if the flow of data from the PC to the modem stops (in both
Voice Command mode and Data mode) for a specified amount of time.
When this timer expires, the modem switches to Data mode with autobauding. By switching to
autobauding (and Data mode), the PC is allowed voice-unaware software to recover control of the
modem in the event of catastrophic failure that does not result in a modem power down. It is
recommended that the PC software leave the modem in autobauding (and Data mode), and use
the Inactivity Timer only as needed. Leaving the modem in autobauding is an extra measure to
prevent confusion from voice-unaware software accessing the modem in Voice mode at a fixed
PC/modem interface rate. You can use the H command to switch to autobauding and Data mode
automatically. In Voice mode, the modem does not allow the auto answer feature, since this feature
does not allow the PC to set the modem in Voice mode before answering the phone.
Command: +VLS=<label> Select Analog Source/Destination
Result Codes: OK if command accepted; ERROR if the <label> parameter is out of range or if the modem cannot
service the <label> parameter requested.
Description: The +VLS= command causes the modem to select one or more source and destination devices for
the analog data to be transmitted. The parameter <label> is used to identify each of the supported
analog source/destination hardware devices. Codes, called "primitives", are provided to describe
which voice I/O device(s) are components in a possible hardware configuration. The codes are
grouped to help define and label 16 common hardware configurations. Each code, except "L" and
"T" is followed by an ASCII 0 code (20 hex). Two codes can be concatenated to define a possible
analog source/destination hardware configuration.
Code Description
L Local phone (no number code)
T Telco line (no number code)
M0 Internal microphone
M1 External microphone
S0 Internal speaker (requires squelch on any microphone activity)
S1 External speaker (requires squelch on any microphone activity)
H0 External microphone and speaker combination (handset or headset)
Zn Manufacturer specific device (n>0)
Mn Manufacturer specific extension (n>1)
Sn Manufacturer specific extension (n>1)
Hn Manufacturer specific extension (n>0)
The list below contains 16 commonly used hardware configurations, and the label and codes used
to select each configuration.
<label> Code(s)
Description
0 none Modem on-hook. Local phone connected to Telco.
1 T Modem off-hook, and connected to Telco. Local phone provided with power
to detect hook condition.
2 L Modem off-hook. Local phone connected to modem.