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16–9
whereby <CM> represents a two-letter command syntax. A value string consists of
values separated by commas or semicolons. The first two command forms are for
read actions, the last two are for write actions. A command line may have both ac-
tion types or be just a read or write type only.
Response Syntax
For each command line received, the modem issues a response to each command in
the command line followed by a final response.
Each command response is of the form:
<CR><LF>
<value> (or) <value range> (response to ? or =? command)
<CR><LF>
The final response is
<CR><LF>
OK (or) ERROR (Command line response)
<CR><LF>
The ASCII character combination <CR><LF> is not shown in the explanations
below. The final response is OK if all the commands in the command line have been
successfully executed, otherwise it is ERROR.
Flow Control
Flow Control is necessary to match the DTE-DCE data rate to the line signaling
rate and to the requirements of analog conversion of the voice signals and data. For
ZyXEL 2864 series modems, both software XON/XOFF and hardware RTS/CTS
flow control are used whereas the software flow control is the default setting. The
DTE may turn off the flow control, but some other method must be used to avoid
overrun of the buffer.
The DTE can select the flow control method in voice mode by using the +FLO
command (defined in Class 2 and 2.0).
Supported Commands For Voice Mode Operation
• ATD (with +FCLASS=8)
This command causes the DCE to dial a phone number. The DCE uses the current
destination setting to perform a dial action. If +VLS is equal to zero at the time of
the ATD command, the DCE will return an ERROR result code.
The DCE attempts to determine when the remote station has gone off-hook by uti-
lizing ringback detection and disappearance (see the +VRA and +VRN commands,
respectively). Once the DCE has determined with high confidence that the remote
station has gone off hook, the DCE returns the OK result code. For example, the