Specifications

MultiModem ISI Hybrid Series, ISIHI-2S/2U 69
Chapter 4—MODEM AT Commands, S-Registers, Result Codes
A parameter after a command (0, 1, 2, etc.) tells the modem which option to use. If you
do not specify a parameter, the modem assumes the 0 (zero) option. E, for example, is the
same as E0. You can issue several commands on a single line (a command string) as long
as the line does not exceed 40 characters.
Note: Each character in a command counts toward the 40 character command line
maximum. Example: Q1 is a single command, but it counts as two characters in the
command line.
Each command has a valid range of parameters. For example, &S can have only 0 or 1 as
a parameter. Valid commands always generate an OK result code, and a few generate an
additional response such as a list of parameters. An invalid command such as &S3, which
has a parameter outside the valid range, generates an ERROR result code. Most
commands have a default parameter that is enabled when the modem is turned on or reset
with the ATZ or AT&F command. Factory defaults are stored in read-only memory
(ROM) and cannot be changed. User-defined defaults can be stored in nonvolatile
random-access memory (NVRAM) and can be changed or deleted at will.
Command Editing
Always begin a command with the letters AT. Enter the entire command string in upper or
lower case, but do not mix cases within the command string. The AT command is not
executed until you press ENTER. Use the BACKSPACE key to erase the previous
command character. It will not erase the AT characters once they are typed. If your
keyboard has no BACKSPACE key, use CTRL+H. (You can change the character
recognized by the modem as BACKSPACE to any other ASCII character by changing
register S5.)
Press CTRL+X to cancel an entire command that has been typed but not yet executed.
This also clears the command buffer. The effect is the same as backspacing the command,
only quicker.
The modem stores characters entered in a command in its command buffer until they are
executed by pressing ENTER. The command buffers capacity is 40 characters. The
attention characters (AT) do not count toward the 40-character command line maximum.
You may use spaces for increased readability when typing a command. Spaces are not
stored in the command buffer, and they do not count towards the 40-character command
line maximum. Special characters, such as hyphens and parentheses, are not allowed.
If you exceed the 40-character limit or type invalid characters, the command buffer is
automatically erased and an ERROR message appears. Retype the command within the
40-character limit, using only the allowed characters.
The commands in this chapter are organized by function. Abbreviated commands are
listed on the next page by function along with a short description and page numbers that
refer to a more detailed description, immediately following this list.