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AT Commands
Page 63
V.25bis Operations
V.25bis is a modem command set like the AT command set, which allows you to control your
modem. However, V.25bis commands may be issued to the modem in asynchronous or
synchronous mode (AT commands may only be issued when the modem is operating in
asynchronous mode). This means V.25bis is suitable for mainframe and minicomputers which
only support synchronous communications ports. The implementation of V.25bis supported by
your modem is based upon the 1988 revision of the V.25bis specification, however not all
aspects of the V.25bis specification have been implemented.
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V.25bis operation is supported in both smart and dumb modes.
Selecting V.25bis Operation
To select V.25bis mode, issue the appropriate #M command. Three V.25bis modes are supported
by your modem:
o Asynchronous V.25bis. The modem operates in asynchronous mode using V.25bis command
rather than AT commands. Issue the AT#M1 command to select this mode.
o Synchronous V.25bis with HDLC framing. The modem communicates and accepts V.25bis
commands in synchronous mode with HDLC framing. Issue the AT#M2 command to select
this mode.
o Synchronous V.25bis/BSC mode. The modem communicates and accepts V.25bis commands
in synchronous mode with character framing (BSC mode). Issue the AT#M3 command to
select this mode.
The &W and Z commands must be issued after the #M command in order for V.25bis command
mode to be selected. Alternately, issue the &W command after the #M command and switch the
modem off and on or lower DTR (after an &D3 command has been issued).
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When you reset the modem (for example, you issue the &F command or issue the RST
command or switch the modem off and on), you must issue an ATZ command to select
V.25bis command mode; your modem always resets and powers-up in AT command mode,
regardless of the setting of the #M command.
If your modem has Option switches to select V.25bis operation, the setting of the Option
switches always take precedence over the #M command.
The %R2 option will be required for most V.25bis setups. This setting ensures that the CTS
signal is only asserted when the modem is ready to accept a new command (in command mode).