Apple Express Fax/Modem - Manual (Page 128)

The commands can be either upper or lowercase characters. However, both
attention characters must be in the same case (for example, AT or at). The
modem must be in command state to recognize and execute these commands,
with the exception of the escape sequence.
When a line of commands is executed, only the last result code for the
command is displayed. If any command needs to display information
different from the result code, it will be displayed. All intermediate result
codes are canceled.
Interpreting the default
If a value required for a particular command is not supplied, your modem
will normally interpret the value as 0. The value supplied by the modem
when you do not alter it is called the default. It’s the value the modem
assumes when you first start it up or after the original factory settings are
restored. You can restore the original settings by using the AT&F command
described later.
Interpreting valid parameter ranges
Some commands are accompanied by options, typically 0 and 1. An italic n
appears beside the title of a command to indicate the availability of these
optional settings. If you use one of these commands without a number, the
modem assumes the value to be 0. Every optional value is evaluated in
modulo 256. For example, ATE1 yields the same result as ATE257 because
(1 mod 256) = (257 mod 256) = 1. After evaluating the argument modulo 256,
if the value is not supported then ERROR is returned. Any argument greater
than 999 in a command will generate an ERROR result code.
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