Credits
 Introduction.
 HAYES-clones.
 The HAYES set.
 The Physical DCE/DTE-lines.
 The telephone line.
 The modulation frequencies and call setup phase tones.
 For the F(requency) S(hift) K(eying) methodes.
 Automatic answering sequence (V25).
 For  the D(iferential) P(hase) S(hift)  K(eying)
 Automatic answering mode V22(bis).
 Some advise on real physical level.
 Connection of the terminal to the HAYES.
 The differences in the Hayes command set.
 Appendix A.  Datascope.