At Command Summary - 3Com 3C900B Installation And Operating Instructions Manual

AT Command Summary

Type commands in either upper or lower case, not a combination. Use the
Backspace key to delete errors. (You cannot delete the original AT command since
it is stored in the modem buffer.)
If a command has numeric options and you don't include a number, zero is
assumed. For example, if you type ATB, the command ATB0 is assumed.
Every command except A/, A>, and +++ must begin with the AT prefix and be entered
by pressing ENTER.
The maximum command length is 58 characters. The modem doesn't count the AT prefix,
carriage returns, or spaces.
NOTE:
All defaults are based on the &F1 Hardware Flow Control template
loaded in NVRAM when the modem is shipped. Defaults are listed in italics.
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T Q R
ECHNICAL UICK EFERENCE