User's Manual

15
4) Toggling the DTR signal (Pin #6) from On to Off can be used to put the module in
either the On Line Command Mode or Off Line Command Mode. If AT&D1 is set
and the DTR signal is turned off, the module will enter the On Line Command Mode
and will require an ATO to return on line or an ATH to disconnect. If AT&D2 is set
and DTR is turned off, the module will enter the Off Line Command Mode. To enter
the On Line Data Mode, DTR must be turned on and a new connection must be
established with the “ ATA” or “ ATD” commands.
The AT Command Set
Controlling the WHM900 functions is accomplished by issuing “AT” commands from
the Host equipment. The module will automatically accept and process “AT” commands
at 1200, 2400, 9600, 19.2K, or 57.6K (Bits per second). This speed is commonly referred
to as the DTE (Data Terminal Equipment) speed. The Parity setting MUST be 8 data bits,
No Parity, and 1 stop bit (8N1). For each command issued, the module will respond with
a result code informing you of the modules status. The format of a basic “ AT” command
and result code is as follows:
AT <Command> <CR>
OK
Meaning:
AT = ATtention what follows is a command
<Command> = any valid command or parameter
<CR> = Carriage Return or Enter Key to process the preceding “ AT” command
OK = AT Command Result code meaning that the module has accepted the command
The command line length is the “ AT” plus 40 additional commands or parameters plus
the Carriage Return character. This means that no command line may exceed a total of 43
total characters. Exceeding the command line length limit or entering an invalid AT
command string will cause the module to respond with the “ ERROR” result code.