1.AT% Commands Enable/Disable Data Compression

2.1.ERROR DETECTION AND DATA COMPRESSION COMMANDS

2.1.1.AT% Commands

%C - Enable/Disable Data Compression

Enables or disables data compression negotiation. The modem can only perform data compression on an error-corrected link.

%C0	Disables data compression (default)
%C2	Enables V.42bis data compression
%C3	Enables V.42bis data compression

Note that HardModems typically support MNP5 with %C1 and MNP5 or V.42bis with %C3.

2.2.AT COMMAND RESULT CODES

The modem AT command handler responds to commands from the caller and to activity on the line via result codes. The possible result codes that the modem can send are listed below.

Two forms of each result code are available: long-form, "verbose" response when V1 is selected, and short-form, a data-like numeric response (included in parentheses following the long-form) when V0 is selected. The long-form code is preceded and terminated by the sequence <CR> <LF>. The short-form is terminated by <CR> only with no preceding sequence. If result messages are suppressed, nothing is returned to the caller.

OK (0)

The OK code is returned by the modem to acknowledge execution of a command line.

CONNECT (1)

The modem will send this result code upon connecting when the line speed is 300bps and the modem has been instructed to report the line speed upon connecting, or the range of result code responses is restricted by the X command such that no speed reporting is allowed.

RING (2)

The modem sends this result code when incoming ringing is detected on the line as per the interface description.

NO CARRIER (3)

The modem sends this result code when attempting to establish a call if no ringback is detected within the period of time determined by register S7. It is also used when the modem auto-disconnects due to loss of carrier.

Under X0, if busy tone detection is enforced, this result code is used as a response to the detection of busy or reorder. Under X0, if dial tone detection is enforced or selected, this result code is used to indicate that dial tone has not been detected.

ERROR (4)

The modem returns this result code if the command line contains a syntax error or it is unable to execute a command contained in the command line. It is issued if a command does not exist or if the parameter supplied is outside the permitted range.

Under X0, X1, X2, and X3, this result is used instead of DELAYED and BLACKLISTED.

CONNECT 1200 (5)

For X1, X2, X3, and X4, The modem sends this result code when the line speed is 1200bps and The modem has been instructed to report the line speed upon connecting.