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DEFINITY Communications System
CHAPTER 4: OPERATION AND CONFIGURATION
7400B Data Module
User’s Guide
Page 4-3
In command mode, the 7400B Data Module looks at everything you
type on your keyboard. When you type in something that the data
module recognizes as a valid command with a valid parameter (if
required), it will execute the action requested. A valid command with
an invalid parameter will produce the ERROR result code, and an invalid
command is simply ignored.
In on-line mode, everything you type is passed as data without
interpretation by the 7400B Data Module, except the escape sequence.
The escape sequence, described in later paragraphs, provides a way of
switching the data module back to command mode without
disconnecting a data call.
ISSUING COMMANDS
The following paragraphs describe the elements of a command line and
how the 7400B Data Module responds to a command line when it is
issued.
Command Line Prefix
All commands issued to the 7400B Data Module, except the escape
sequence and the repeat command, must begin with the letters “AT”.
This is called the command line prefix and must be entered as either
both uppercase or both lowercase letters (that is, at and AT will work,
but aT or At will not).
The AT prefix (also known as the ATtention command) alerts the data
module to expect one or more commands to follow. Each time the AT
prefix is sent, the data module adjusts its speed and parity to match your
local terminal.
Command Buffer As you type in a command, each character is saved in a 40-character
buffer. The
AT
prefix, spaces, and the
[ Enter ]
at the end of the command
line are not saved and do not add to the character count. If you try to
type more than 40 countable characters on one line, the result code
ERROR will be displayed on your terminal screen, and the command
line will be ignored.
Command Line Set Up A command line begins with the AT prefix, includes one or more
commands, and finishes with a line termination, usually issued by
pressing the
[ Enter ]
key. The factory-default line termination character
is an ASCII carriage return, represented by the decimal number 013
stored in S-register S03.