IBM 2193 - Manual (Page 188)

B-8 IBM Personal Computer User Guide
Table1: AT commands (Continued)
Command Function
X1 Same as X0 plus all CONNECT responses/blind dialing
X2 Same as X1 plus dial tone detection
X3 Same as X1 plus busy signal detection/blind dialing
X4 All responses and dial tone and busy signal detection
Z Reset and recall user profile