IBM 2193 - Manual (Page 193)

Modem information B-13
S registers
S registers are information storage areas inside the modem. The AT command set
uses the S registers to configure modem options. Some S registers have default
settings. For normal modem operations, the default settings are usually adequate.
However, special circumstances may require you to change some defaults. To
change or read the value of an S register, begin the command with the letters AT.
To read the value of an S register:
• Use the ATSr? command (r=register number 0-28).
For example, to read the value of S register 0, type ATS0? and press Enter.
To change the value of an S register:
• Use the ATSr=n command (r=register number 0-28, n=the new value you want
to assign).
For example, to change the value of S register 0 to 20 rings, type ATS0=20 and
press Enter.