Apple Express Fax/Modem - Manual (Page 129)

Setting the S registers
The S command is used to assign values to various registers in the modem’s
memory. Most of the S registers deal with certain aspects of timing. You can
customize the behavior of the modem by setting the values in the S registers.
Whatever the setting of register S3, the character (ASCII 13) is always
recognized. The option in the Set Register command (S
n=) is also evaluated
modulo 256 before setting the register to the new value. See the S registers
for details of the effects of setting a given register value out of range.
Any attempt to set or read a reserved or unused register will generate an
ERROR.
AT command set
AT refers to the command prefix (attention sequence) that precedes each
command to the modem. With the exception of A/, all commands must be
preceded by AT and end with a carriage return . In this appendix, the
modem’s default value and description are shown in boldface type.
Special Commands
A/ Repeat last command The A/ command instructs the modem to repeat
the last command line. A command line termination character is
not required for the execution of this command that is; the command is
executed as soon as the slash is typed.
+++ Return to command state (escape sequence) The escape sequence is
used to force the modem back to local command state from on-line
state. Do not type any other commands or make entries before or after
the escape sequence for a period equal to the guard time set in register
S12 (default is one second).
The modem sends an OK result code to the terminal and switches to
command state.
The actual escape character is specified by register S2, expressed as the
ASCII value of the escape character (default is 43=+).
117 M O D E M C O M M A N D S E T