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22 Basic Modem Operation
modem uses. By default, your modem uses result codes equivalent
to the ATX5 command.
The result code options will be covered more thoroughly in later
chapters.
Viewing S Register Values
Status registers (or "S-registers") contain values that determine the
modem’s operating characteristics. Whenever you send an AT
command to your modem, you are actually changing the value of an
S-register.
You can use the Sr? command to view the value of S-register ‘r’.
For example, to view the value of S-register S0, which controls
auto-answering, type ATS0? and press Enter. The modem responds
with a three-digit character showing the value of this register,
followed by OK. A value of 002, for example, means your modem
will auto-answer incoming calls after the second ring.
Some S-registers are bit mapped. For these registers, you can use
the Sr.b? command to read their values.
For example, to read the value of S-register S35, bit 7, type
ATS35.7? and press Enter. The modem responds with an
appropriate value, followed by OK.
Changing S Register Values
You can use the ATS0=n command to change the value of an S-
register.
For example, to have your modem auto-answer an incoming call
after two rings, set S-register 0 to 2. Be sure the n value is between
1 and 255. If n is set to 0, your modem will not answer incoming
calls.