Answering From Synchronous Mode; Auto-Answer; Manual Answer - ZyXEL Communications U-336S User Manual

Answering from Synchronous Mode

Auto-Answer

Set the modem to synchronous mode. Set the S-register S0 to equal
the number of rings before auto-answer occurs. Set it from the
terminal (if &M1 is set) using the asynchronous AT command, or
select the STATUS REGISTER menu to change the S0 value.

Manual Answer

Type ATA from the terminal (if &M1 is set).
42 LCD Panel Operation