3Com 1.024.1644-00 manual Timer

			Technical Reference
Register	Default	Function
S19	0	Sets the duration, in minutes, for the inactivity timer. The
		timer activates when there is no data activity on the phone
		line; at time-out the modem hangs up. S19 = 0 disables
		the timer.
S20	0	Reserved
S21	10	Sets the length, in 10-millisecond units, of breaks sent
		from the modem to the computer; applies to MNP or
		V.42 mode only.
S22	17	Stores the ASCII decimal code for the XON character.
S23	19	Stores the ASCII decimal code for the XOFF character.
S24	0	Reserved
S25	20	Sets the duration, in hundredths of a second, that DTR
		must be dropped so that the modem does not interpret a
		random glitch as a DTR loss. (Most users will want to use
		the default; this register is useful for setting compatibility
		with older systems running under older operating software.)
S26	0	Reserved
S27	0	Bit-mapped register setup. To set the register,
		see instructions for S13.
		Bit	Value	Result
		0	1	Enables ITU-T V.21 modulation at 300
				bps for overseas calls; in V.21 mode,
				the modem answers both overseas
				and domestic (U.S. and Canada)
				calls, but only originates V.21 calls.
				(Default Bell 103)
		1	2	Enables unencoded (non-trellis
				coded) modulation in V.32 mode.

68 56K Voice Faxmodem Internal - User’s Guide