
Chapter 1 – AT Commands, S-Registers, and Result Codes
Multi-Tech Systems, Inc. AT Commands for the MultiModem & SocketModem MT9234 Series (S000434H) 21
%C Data Compression Control
Description: Use this command to enable or disable data compression. This command enables or
disables V.44, V.42 bis, and MNP class 5 data compression. The command
overwrites the current status of the +DCS command. The command is also
overwritten by changes made by the +DCS command. On-line changes do not take
effect until a disconnect occurs.
Syntax: AT%C<value>
Values: 0 Disable V.42bis/MNP 5. No data compression.
1 Enable V.42bis/MNP 5. Data compression enabled.
Default: 1
Result Codes: OK if <value> = 0, 1.
ERROR if <value> ≠ 0, 1.
%DC AT Command Control
Description: Use this command to set whether or not the modem will respond to AT commands.
Note: This command does not work with parallel, USB, PCI, PCIe.
Syntax: AT%DC<value>
Values: 0 The modem responds to AT commands. The modem will respond to
AT%DC for 10 seconds after it is turned on.
1 The modem ignores AT commands.
Default: 0
%DT Set AT Command Mode Timer
Description: Sets the length of time that the command mode will be disabled when set for %DC1
(the modem ignores AT commands).
Note: This command does not work with parallel, USB, PCI, PCIe.
Syntax: AT%DT<value>
Values: 0-255 in 1 second increments
Default: 0
%E Fallback and Fall Forward Control
Description: This command provides the option for the modem to automatically monitor line
quality, to fall back when line quality is insufficient, and to fall forward when line
quality is sufficient.
Syntax: AT%E<value>
Values: 0 Disable fallback and fall forward.
1 Enable fallback and disable fall forward.
2 Enable fallback and fall forward.
Default: 2
Result Codes: OK if <value> = 0, 1, 2.
ERROR if <value> ≠ 0, 1, 2.
%H Set Callback Security – Direct Connect Enable
Description: Sets Callback Security to normal operation or to direct connect.
Note: This command does not work with parallel, USB, PCI, PCIe.
Syntax: AT%H<value>
Values: 0 Sets callback security to normal operation.
1 All callback security calls will be direct connect regardless of whether the
password or phone number has the - character.
Default: 0
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