Lucent Technologies 7400B manual Issuing Commands, Command Line Prefix, Command Buffer

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 AT tention 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.