Specifications

February 23, 2000 Motorola Personal Communications Sector Page 4
Satellite Subscriber Products Division
Motorola Personal Communications Sector
Satellite Subscriber Products Division
ISU AT Command Reference Modem Overview
2 Modem Overview
2.1 DTE-ISU Interchange Circuits
The communication between the ISU and the DTE follows the ITU-T V.24 (RS-232) recommendation.
Please see reference [7] for details.
2.2 Mode of Operation
The ISU is always in one of two modes - command mode or data mode.
When the ISU is in command mode (or off-line mode), AT commands can be entered to control the phone.
When in data (also called on-line) mode, the ISU is connected to a remote system and any characters sent to
it will be transmitted to the remote system. It is possible to enter the command mode without terminating the
call by using the +++ escape sequence detailed below.
2.3 Command and Response Characters
The ASCII character set (CCITT T.50 International Alphabet 5, American Standard Code for Information
Interchange) is used for the issuance of commands and responses. Only the low-order 7 bits of each charac-
ter are used for commands or parameters; the high-order bit is ignored. Upper case characters are equivalent
to lower case characters.
2.4 Command Entry
An AT command is a string of characters sent by the DTE to the ISU while the ISU is in command mode. A
command string has a prefix, a body, and a terminator. The prefix consists of the ASCII characters AT or at.
The body is a string of commands restricted to printable ASCII characters.The default terminator is the
<CR> character.
There are two format types for AT commands: basic and extended. The basic commands consist of single
ASCII characters, or single characters preceded by a prefix character, followed by a decimal parameter.
Examples of these commands are in section 3. Extended commands are action or parameter commands for
which a special syntax is used. The commands in section 4 through section 9 are of this type.
There are a few rules about the entry of commands:
• All commands (apart from A/ and +++) start with AT or at. The commands in a command string (apart
from A/ and +++) are executed only after the return or enter key is pressed.
• Use all upper or lower case letters, not a combination.
• The maximum number of characters in a command string is 128. Multiple commands can be concate-
nated onto a single command line or by a semicolon.
• Command editing can usually be performed by the backspace or delete keys.
• If a parameter is missed from a basic command, a zero is implied (e.g. ATH implies ATH0). If an
optional parameter is skipped from an extended command, the current value is implied. Optional param-
eters are enclosed by square brackets ([...]) in this document.
• Spaces can be entered into a command string to increase clarity. These are ignored.
• Characters that precede the AT prefix are ignored.
• Ctrl-x can be used to abort a command line input.