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Operation
Command Mode Overview
When in command mode, the modem can accept AT commands which determine how it will
perform those essential functions.
Command Mode Basics
•
To use AT commands requires a computer or terminal at the DTE port with an EIA/TIA-232-
F serial port to enable communication between the DTE and the modem. If a computer is the
DTE, it will also require a communications software package. Any error correction or data
compression software used by the computer must support flow control.
•
When powered up, the modem is in command mode. It enters data mode when you command
it to go on-line to another modem by dialing a switched network connection or initiating
handshake for a private line connection. The modem can also enter data mode when it goes on-
line in response to a connection initiated by a remote modem.
•
Command mode is always asynchronous; data mode can be either asynchronous or
synchronous.
•
The AT&M command can configure the modem for asynchronous operation in both modes, or
for asynchronous operation in command mode and synchronous operation in data mode.
•
Depending on its option settings, you can set the modem to enter command mode and wait for
the next AT command by one of three methods:
•
Using AT&D1 command
•
Dropping DTR
•
Typing the Escape sequence (+++)
Automatic DTE Speed and Parity Detection
The modem is shipped with the DTE interface set for 7 bits with parity at the last AT speed. This
determines the modem's DTE speed when auto answering. In command mode the modem
automatically detects the DTE's operating speed and asynchronous character parity (ODD, EVEN,
SPACE, or MARK/NONE parity) when it receives the AT prefix from the DTE. The modem can
automatically adapt to character length and parity of the incoming data at any of the following
asynchronous bit rates:
128,000 bps
76,800 bps
56,000 bps
32,000 bps
24,000 bps
14,400 bps
4800 bps
Note
Configuration via the
At 1200 bps the modem can be configured to use either ITU-T V.22 or Bell 212A modulation. At 300 bps
the modem can be configured to use either ITU-T V.21 or Bell 103 modulation.
060R122-000
Issue 15
115,200 bps
112,000 bps
72,000 bps
64,000 bps
48,000 bps
38,400 bps
31,200 bps
28,800 bps
21,600 bps
19,200 bps
12,000 bps
9600 bps
2400 bps
1200 bps
&H
command determines modem modulation at a DTE speed of 1200 or 300 bps.
SpectraComm Dual V.34 Modem
Installation and Operation
Command Mode Overview
96,000 bps
57,600 bps
33,600 bps
26,400 bps
16,800 bps
7200 bps
300 bps
3-21
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